diff --git a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-debug.js b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-debug.js
index c5b7e404c0f..d79fed4a423 100644
--- a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-debug.js
+++ b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-debug.js
@@ -57,12 +57,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             return;
         }
 
-        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
-            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
-            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
-            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
-
-        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+        if (!this.shouldLockScroll(forceOnSmallWindow)) {
             Y.log('Dialogue height greater than window height. Ignoring enable request.', 'warn', 'moodle-core-lockscroll');
             return;
         }
@@ -96,6 +91,44 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
         return this;
     },
 
+    /**
+     * Recalculate whether lock scrolling should be on or off.
+     *
+     * @method shouldLockScroll
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @return boolean
+     */
+    shouldLockScroll: function(forceOnSmallWindow) {
+        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
+            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
+            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
+            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
+
+        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+            return false;
+        } else {
+            return true;
+        }
+    },
+
+    /**
+     * Recalculate whether lock scrolling should be on or off because the size of the dialogue changed.
+     *
+     * @method updateScrollLock
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @chainable
+     */
+    updateScrollLock: function(forceOnSmallWindow) {
+        // Both these functions already check if scroll lock is active and do the right thing.
+        if (this.shouldLockScroll(forceOnSmallWindow)) {
+            this.enableScrollLock(forceOnSmallWindow);
+        } else {
+            this.disableScrollLock(true);
+        }
+
+        return this;
+    },
+
     /**
      * Stop locking the page scroll.
      *
@@ -105,7 +138,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
      * @method disableScrollLock
      * @chainable
      */
-    disableScrollLock: function() {
+    disableScrollLock: function(force) {
         if (this.isActive()) {
             Y.log('Disabling LockScroll.', 'debug', 'moodle-core-lockscroll');
             this._enabled = false;
@@ -117,7 +150,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             var currentCount = parseInt(body.getAttribute('data-activeScrollLocks'), 10) || 1,
                 newCount = currentCount - 1;
 
-            if (currentCount === 1) {
+            if (force || currentCount === 1) {
                 body.removeClass('lockscroll');
                 body.setStyle('maxWidth', null);
             }
diff --git a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-min.js b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-min.js
index 5207360b5d0..e7d7c8ab861 100644
--- a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-min.js
+++ b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll-min.js
@@ -1 +1 @@
-YUI.add("moodle-core-lockscroll",function(e,t){e.namespace("M.core").LockScroll=e.Base.create("lockScroll",e.Plugin.Base,[],{_enabled:!1,destructor:function(){this.disableScrollLock()},enableScrollLock:function(t){if(this.isActive())return;var n=this.get("host").get("boundingBox").get("region").height,r=e.config.win.innerHeight||e.config.doc.documentElement.clientHeight||0;if(!t&&n>r-10)return;this._enabled=!0;var i=e.one(e.config.doc.body),s=i.getComputedStyle("width");i.addClass("lockscroll");var o=parseInt(i.getAttribute("data-activeScrollLocks"),10)||0,u=o+1;return i.setAttribute("data-activeScrollLocks",u),o===0&&i.setStyle("maxWidth",s),this},disableScrollLock:function(){if(this.isActive()){this._enabled=!1;var t=e.one(e.config.doc.body),n=parseInt(t.getAttribute("data-activeScrollLocks"),10)||1,r=n-1;n===1&&(t.removeClass("lockscroll"),t.setStyle("maxWidth",null)),t.setAttribute("data-activeScrollLocks",n-1)}return this},isActive:function(){return this._enabled}},{NS:"lockScroll",ATTRS:{}})},"@VERSION@",{requires:["plugin","base-build"]});
+YUI.add("moodle-core-lockscroll",function(e,t){e.namespace("M.core").LockScroll=e.Base.create("lockScroll",e.Plugin.Base,[],{_enabled:!1,destructor:function(){this.disableScrollLock()},enableScrollLock:function(t){if(this.isActive())return;if(!this.shouldLockScroll(t))return;this._enabled=!0;var n=e.one(e.config.doc.body),r=n.getComputedStyle("width");n.addClass("lockscroll");var i=parseInt(n.getAttribute("data-activeScrollLocks"),10)||0,s=i+1;return n.setAttribute("data-activeScrollLocks",s),i===0&&n.setStyle("maxWidth",r),this},shouldLockScroll:function(t){var n=this.get("host").get("boundingBox").get("region").height,r=e.config.win.innerHeight||e.config.doc.documentElement.clientHeight||0;return!t&&n>r-10?!1:!0},updateScrollLock:function(e){return this.shouldLockScroll(e)?this.enableScrollLock(e):this.disableScrollLock(!0),this},disableScrollLock:function(t){if(this.isActive()){this._enabled=!1;var n=e.one(e.config.doc.body),r=parseInt(n.getAttribute("data-activeScrollLocks"),10)||1,i=r-1;if(t||r===1)n.removeClass("lockscroll"),n.setStyle("maxWidth",null);n.setAttribute("data-activeScrollLocks",r-1)}return this},isActive:function(){return this._enabled}},{NS:"lockScroll",ATTRS:{}})},"@VERSION@",{requires:["plugin","base-build"]});
diff --git a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll.js b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll.js
index c15b74eabc0..e447cd16871 100644
--- a/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll.js
+++ b/lib/yui/build/moodle-core-lockscroll/moodle-core-lockscroll.js
@@ -56,12 +56,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             return;
         }
 
-        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
-            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
-            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
-            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
-
-        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+        if (!this.shouldLockScroll(forceOnSmallWindow)) {
             return;
         }
 
@@ -91,6 +86,44 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
         return this;
     },
 
+    /**
+     * Recalculate whether lock scrolling should be on or off.
+     *
+     * @method shouldLockScroll
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @return boolean
+     */
+    shouldLockScroll: function(forceOnSmallWindow) {
+        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
+            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
+            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
+            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
+
+        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+            return false;
+        } else {
+            return true;
+        }
+    },
+
+    /**
+     * Recalculate whether lock scrolling should be on or off because the size of the dialogue changed.
+     *
+     * @method updateScrollLock
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @chainable
+     */
+    updateScrollLock: function(forceOnSmallWindow) {
+        // Both these functions already check if scroll lock is active and do the right thing.
+        if (this.shouldLockScroll(forceOnSmallWindow)) {
+            this.enableScrollLock(forceOnSmallWindow);
+        } else {
+            this.disableScrollLock(true);
+        }
+
+        return this;
+    },
+
     /**
      * Stop locking the page scroll.
      *
@@ -100,7 +133,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
      * @method disableScrollLock
      * @chainable
      */
-    disableScrollLock: function() {
+    disableScrollLock: function(force) {
         if (this.isActive()) {
             this._enabled = false;
 
@@ -111,7 +144,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             var currentCount = parseInt(body.getAttribute('data-activeScrollLocks'), 10) || 1,
                 newCount = currentCount - 1;
 
-            if (currentCount === 1) {
+            if (force || currentCount === 1) {
                 body.removeClass('lockscroll');
                 body.setStyle('maxWidth', null);
             }
diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
index b94fdf9bd92..86f372cba1c 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-debug.js
@@ -331,6 +331,11 @@ Y.extend(DIALOGUE, Y.Panel, {
                                 'height' : this.get('height')});
             }
         }
+
+        // Update Lock scroll if the plugin is present.
+        if (this.lockScroll) {
+            this.lockScroll.updateScrollLock(this.shouldResizeFullscreen());
+        }
     },
     /**
      * Center the dialog on the screen.
@@ -387,13 +392,6 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.get('boundingBox').setXY(this._originalPosition);
         }
 
-        // Lock scroll if the plugin is present.
-        if (this.lockScroll) {
-            // We need to force the scroll locking for full screen dialogues, even if they have a small vertical size to
-            // prevent the background scrolling while the dialogue is open.
-            this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
-        }
-
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);
diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
index db5eca8027c..bdbf8f36a79 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue-min.js
@@ -1,2 +1,2 @@
-YUI.add("moodle-core-notification-dialogue",function(e,t){var n,r,i,s,o,u,a;n="moodle-dialogue",r="notificationBase",i="yesLabel",s="noLabel",o="title",u="question",a={BASE:"moodle-dialogue-base",WRAP:"moodle-dialogue-wrap",HEADER:"moodle-dialogue-hd",BODY:"moodle-dialogue-bd",CONTENT:"moodle-dialogue-content",FOOTER:"moodle-dialogue-ft",HIDDEN:"hidden",LIGHTBOX:"moodle-dialogue-lightbox"},M.core=M.core||{};var f="Moodle dialogue",l,c=n+"-fullscreen",h=n+"-hidden",p=" [role=dialog]",d="[role=menubar]",v=".",m="moodle-has-zindex",g='input:not([type="hidden"]), a[href], button, textarea, select, [tabindex]';l=function(t){var n=e.clone(t);n.COUNT=e.stamp(this);var r="moodle-dialogue-"+n.COUNT;n.notificationBase=e.Node.create('<div class="'+a.BASE+'">').append(e.Node.create('<div id="'+r+'" role="dialog" '+'aria-labelledby="'+r+'-header-text" class="'+a.WRAP+'"></div>').append(e.Node.create('<div id="'+r+'-header-text" class="'+a.HEADER+' yui3-widget-hd"></div>')).append(e.Node.create('<div class="'+a.BODY+' yui3-widget-bd"></div>')).append(e.Node.create('<div class="'+a.FOOTER+' yui3-widget-ft"></div>'))),e.one(document.body).append(n.notificationBase),n.additionalBaseClass&&n.notificationBase.addClass(n.additionalBaseClass),n.srcNode="#"+r,n.closeButton===!1?n.buttons=null:n.buttons=[{section:e.WidgetStdMod.HEADER,classNames:"closebutton",action:function(){this.hide()}}],l.superclass.constructor.apply(this,[n]),n.closeButton!==!1&&this.get("buttons").header[0].setAttribute("title",this.get("closeButtonTitle"))},e.extend(l,e.Panel,{_resizeevent:null,_orientationevent:null,_calculatedzindex:!1,_originalPosition:null,_hiddenSiblings:null,initializer:function(){var t;this._hiddenSiblings=[],this.get("render")&&this.render(),this.after("visibleChange",this.visibilityChanged,this),this.get("center")&&this.centerDialogue(),this.get("modal")&&(this.get(r).set("aria-hidden","true"),this.plug(e.M.core.LockScroll)),t=this.get("boundingBox"),t.addClass(m),e.Array.each(this.get("extraClasses"),t.addClass,t),this.get("visible")&&this.applyZIndex(),this.on("maskShow",this.applyZIndex),this.on("maskShow",function(){var t=e.one(e.config.win),n=this.get("boundingBox");this.get("center")||(this._originalPosition=n.getXY()),n.getStyle("position")!=="fixed"&&n.setStyles({top:t.get("scrollTop"),left:t.get("scrollLeft")})},this),this.after("destroyedChange",function(){this.get(r).remove(!0)},this)},applyZIndex:function(){var t=1,n=1,r=this.get("boundingBox"),i=this.get("maskNode"),s=this.get("zIndex");s!==0&&!this._calculatedzindex?r.setStyle("zIndex",s):(e.all(p+", "+d+", "+v+m).each(function(e){var n=this.findZIndex(e);n>t&&(t=n)},this),n=(t+1).toString(),r.setStyle("zIndex",n),this.set("zIndex",n),this.get("modal")&&(i.setStyle("zIndex",n),e.UA.ie&&e.UA.compareVersions(e.UA.ie,9)<0&&setTimeout(function(){i.setStyle("position","static"),setTimeout(function(){i.setStyle("position","fixed")},0)},0)),this._calculatedzindex=!0)},findZIndex:function(e){var t=e.getStyle("zIndex")||e.ancestor().getStyle("zIndex");return t?parseInt(t,10):0},visibilityChanged:function(t){var n,r;t.attrName==="visible"&&(this.get("maskNode").addClass(a.LIGHTBOX),t.prevVal&&!t.newVal&&(r=this.get("boundingBox"),this._resizeevent&&(this._resizeevent.detach(),this._resizeevent=null),this._orientationevent&&(this._orientationevent.detach(),this._orientationevent=null),r.detach("key",this.keyDelegation),this.get("modal")&&this.setAccessibilityHidden()),!t.prevVal&&t.newVal&&(this.applyZIndex(),this.makeResponsive(),this.shouldResizeFullscreen()||this.get("draggable")&&(n="#"+this.get("id")+" ."+a.HEADER,this.plug(e.Plugin.Drag,{handles:[n]}),e.one(n).setStyle("cursor","move")),this.keyDelegation(),this.get("modal")&&this.setAccessibilityVisible()),this.get("center")&&!t.prevVal&&t.newVal&&this.centerDialogue())},makeResponsive:function(){var e=this.get("boundingBox");this.shouldResizeFullscreen()?(e.addClass(c),e.setStyles({left:null,top:null,width:null,height:null,right:null,bottom:null})):this.get("responsive")&&e.removeClass(c).setStyles({width:this.get("width"),height:this.get("height")})},centerDialogue:function(){var t=this.get("boundingBox"),n=t.hasClass(h),r,i;if(this.shouldResizeFullscreen())return;n&&t.setStyle("top","-1000px").removeClass(h),r=Math.max(Math.round((t.get("winWidth")-t.get("offsetWidth"))/2),15),i=Math.max(Math.round((t.get("winHeight")-t.get("offsetHeight"))/2),15)+e.one(window).get("scrollTop"),t.setStyles({left:r,top:i}),n&&t.addClass(h),this.makeResponsive()},shouldResizeFullscreen:function(){return window===window.parent&&this.get("responsive")&&Math.floor(e.one(document.body).get("winWidth"))<this.get("responsiveWidth")},show:function(){var e=null,t=this.headerNode,n=this.bodyNode,r=this.get("focusOnShowSelector"),i=null;return e=l.superclass.show.call(this),!this.get("center")&&this._originalPosition&&this.get("boundingBox").setXY(this._originalPosition),this.lockScroll&&this.lockScroll.enableScrollLock(this.shouldResizeFullscreen()),r!==null&&(i=this.get("boundingBox").one(r)),i||(t&&t!==""?i=t:n&&n!==""&&(i=n)),i&&i.focus(),e},hide:function(e){if(e&&e.type==="key"&&e.keyCode===27&&!this.get("focused"))return;return this.lockScroll&&this.lockScroll.disableScrollLock(),l.superclass.hide.call(this,arguments)},keyDelegation:function(){var e=this.get("boundingBox");e.delegate("key",function(e){var t=e.target,n="forward";e.shiftKey&&(n="backward"),this.trapFocus(t,n)&&e.preventDefault()},"down:9",g,this)},trapFocus:function(e,t){var n=this.get("boundingBox"),r=n.one(g),i=n.all(g).pop();if(e===i&&t==="forward")return r.focus();if(e===r&&t==="backward")return i.focus()},setAccessibilityVisible:function(){var t=this.get(r);e.one(document.body).get("children").each(function(e){if(e!==t){var n=e.get("aria-hidden");n!=="true"&&(e.setData("previous-aria-hidden",n),this._hiddenSiblings.push(e),e.set("aria-hidden","true"))}},this),t.set("aria-hidden","false")},setAccessibilityHidden:function(){var t=this.get(r);t.set("aria-hidden"
+YUI.add("moodle-core-notification-dialogue",function(e,t){var n,r,i,s,o,u,a;n="moodle-dialogue",r="notificationBase",i="yesLabel",s="noLabel",o="title",u="question",a={BASE:"moodle-dialogue-base",WRAP:"moodle-dialogue-wrap",HEADER:"moodle-dialogue-hd",BODY:"moodle-dialogue-bd",CONTENT:"moodle-dialogue-content",FOOTER:"moodle-dialogue-ft",HIDDEN:"hidden",LIGHTBOX:"moodle-dialogue-lightbox"},M.core=M.core||{};var f="Moodle dialogue",l,c=n+"-fullscreen",h=n+"-hidden",p=" [role=dialog]",d="[role=menubar]",v=".",m="moodle-has-zindex",g='input:not([type="hidden"]), a[href], button, textarea, select, [tabindex]';l=function(t){var n=e.clone(t);n.COUNT=e.stamp(this);var r="moodle-dialogue-"+n.COUNT;n.notificationBase=e.Node.create('<div class="'+a.BASE+'">').append(e.Node.create('<div id="'+r+'" role="dialog" '+'aria-labelledby="'+r+'-header-text" class="'+a.WRAP+'"></div>').append(e.Node.create('<div id="'+r+'-header-text" class="'+a.HEADER+' yui3-widget-hd"></div>')).append(e.Node.create('<div class="'+a.BODY+' yui3-widget-bd"></div>')).append(e.Node.create('<div class="'+a.FOOTER+' yui3-widget-ft"></div>'))),e.one(document.body).append(n.notificationBase),n.additionalBaseClass&&n.notificationBase.addClass(n.additionalBaseClass),n.srcNode="#"+r,n.closeButton===!1?n.buttons=null:n.buttons=[{section:e.WidgetStdMod.HEADER,classNames:"closebutton",action:function(){this.hide()}}],l.superclass.constructor.apply(this,[n]),n.closeButton!==!1&&this.get("buttons").header[0].setAttribute("title",this.get("closeButtonTitle"))},e.extend(l,e.Panel,{_resizeevent:null,_orientationevent:null,_calculatedzindex:!1,_originalPosition:null,_hiddenSiblings:null,initializer:function(){var t;this._hiddenSiblings=[],this.get("render")&&this.render(),this.after("visibleChange",this.visibilityChanged,this),this.get("center")&&this.centerDialogue(),this.get("modal")&&(this.get(r).set("aria-hidden","true"),this.plug(e.M.core.LockScroll)),t=this.get("boundingBox"),t.addClass(m),e.Array.each(this.get("extraClasses"),t.addClass,t),this.get("visible")&&this.applyZIndex(),this.on("maskShow",this.applyZIndex),this.on("maskShow",function(){var t=e.one(e.config.win),n=this.get("boundingBox");this.get("center")||(this._originalPosition=n.getXY()),n.getStyle("position")!=="fixed"&&n.setStyles({top:t.get("scrollTop"),left:t.get("scrollLeft")})},this),this.after("destroyedChange",function(){this.get(r).remove(!0)},this)},applyZIndex:function(){var t=1,n=1,r=this.get("boundingBox"),i=this.get("maskNode"),s=this.get("zIndex");s!==0&&!this._calculatedzindex?r.setStyle("zIndex",s):(e.all(p+", "+d+", "+v+m).each(function(e){var n=this.findZIndex(e);n>t&&(t=n)},this),n=(t+1).toString(),r.setStyle("zIndex",n),this.set("zIndex",n),this.get("modal")&&(i.setStyle("zIndex",n),e.UA.ie&&e.UA.compareVersions(e.UA.ie,9)<0&&setTimeout(function(){i.setStyle("position","static"),setTimeout(function(){i.setStyle("position","fixed")},0)},0)),this._calculatedzindex=!0)},findZIndex:function(e){var t=e.getStyle("zIndex")||e.ancestor().getStyle("zIndex");return t?parseInt(t,10):0},visibilityChanged:function(t){var n,r;t.attrName==="visible"&&(this.get("maskNode").addClass(a.LIGHTBOX),t.prevVal&&!t.newVal&&(r=this.get("boundingBox"),this._resizeevent&&(this._resizeevent.detach(),this._resizeevent=null),this._orientationevent&&(this._orientationevent.detach(),this._orientationevent=null),r.detach("key",this.keyDelegation),this.get("modal")&&this.setAccessibilityHidden()),!t.prevVal&&t.newVal&&(this.applyZIndex(),this.makeResponsive(),this.shouldResizeFullscreen()||this.get("draggable")&&(n="#"+this.get("id")+" ."+a.HEADER,this.plug(e.Plugin.Drag,{handles:[n]}),e.one(n).setStyle("cursor","move")),this.keyDelegation(),this.get("modal")&&this.setAccessibilityVisible()),this.get("center")&&!t.prevVal&&t.newVal&&this.centerDialogue())},makeResponsive:function(){var e=this.get("boundingBox");this.shouldResizeFullscreen()?(e.addClass(c),e.setStyles({left:null,top:null,width:null,height:null,right:null,bottom:null})):this.get("responsive")&&e.removeClass(c).setStyles({width:this.get("width"),height:this.get("height")}),this.lockScroll&&this.lockScroll.updateScrollLock(this.shouldResizeFullscreen())},centerDialogue:function(){var t=this.get("boundingBox"),n=t.hasClass(h),r,i;if(this.shouldResizeFullscreen())return;n&&t.setStyle("top","-1000px").removeClass(h),r=Math.max(Math.round((t.get("winWidth")-t.get("offsetWidth"))/2),15),i=Math.max(Math.round((t.get("winHeight")-t.get("offsetHeight"))/2),15)+e.one(window).get("scrollTop"),t.setStyles({left:r,top:i}),n&&t.addClass(h),this.makeResponsive()},shouldResizeFullscreen:function(){return window===window.parent&&this.get("responsive")&&Math.floor(e.one(document.body).get("winWidth"))<this.get("responsiveWidth")},show:function(){var e=null,t=this.headerNode,n=this.bodyNode,r=this.get("focusOnShowSelector"),i=null;return e=l.superclass.show.call(this),!this.get("center")&&this._originalPosition&&this.get("boundingBox").setXY(this._originalPosition),r!==null&&(i=this.get("boundingBox").one(r)),i||(t&&t!==""?i=t:n&&n!==""&&(i=n)),i&&i.focus(),e},hide:function(e){if(e&&e.type==="key"&&e.keyCode===27&&!this.get("focused"))return;return this.lockScroll&&this.lockScroll.disableScrollLock(),l.superclass.hide.call(this,arguments)},keyDelegation:function(){var e=this.get("boundingBox");e.delegate("key",function(e){var t=e.target,n="forward";e.shiftKey&&(n="backward"),this.trapFocus(t,n)&&e.preventDefault()},"down:9",g,this)},trapFocus:function(e,t){var n=this.get("boundingBox"),r=n.one(g),i=n.all(g).pop();if(e===i&&t==="forward")return r.focus();if(e===r&&t==="backward")return i.focus()},setAccessibilityVisible:function(){var t=this.get(r);e.one(document.body).get("children").each(function(e){if(e!==t){var n=e.get("aria-hidden");n!=="true"&&(e.setData("previous-aria-hidden",n),this._hiddenSiblings.push(e),e.set("aria-hidden","true"))}},this),t.set("aria-hidden","false")},setAccessibilityHidden:function(){var t=this.get(r);t.set("aria-hidden"
 ,"true"),e.Array.each(this._hiddenSiblings,function(e){var t=e.getData("previous-aria-hidden");t===null?e.removeAttribute("aria-hidden"):e.set("aria-hidden",t)}),this._hiddenSiblings=[]}},{NAME:f,CSS_PREFIX:n,ATTRS:{notificationBase:{},lightbox:{lazyAdd:!1,setter:function(e){this.set("modal",e)}},closeButton:{validator:e.Lang.isBoolean,value:!0},closeButtonTitle:{validator:e.Lang.isString,value:M.util.get_string("closebuttontitle","moodle")},center:{validator:e.Lang.isBoolean,value:!0},draggable:{validator:e.Lang.isBoolean,value:!1},COUNT:{value:null},responsive:{validator:e.Lang.isBoolean,value:!0},responsiveWidth:{value:768},focusOnShowSelector:{value:null}}}),e.Base.modifyAttrs(l,{width:{value:"400px",setter:function(e){return e==="auto"?"":e}},visible:{value:!1},centered:{setter:function(e){return e&&this.set("center",!0),!1}},render:{value:!0,writeOnce:!0},extraClasses:{value:[]}}),e.Base.mix(l,[e.M.core.WidgetFocusAfterHide]),M.core.dialogue=l;var y=function(){y.superclass.constructor.apply(this,arguments)};e.extend(y,M.core.dialogue,{initializer:function(){this.show()}},{NAME:"Moodle information dialogue",CSS_PREFIX:n}),e.Base.modifyAttrs(y,{modal:{validator:e.Lang.isBoolean,value:!0}}),M.core.notification=M.core.notification||{},M.core.notification.info=y},"@VERSION@",{requires:["base","node","panel","escape","event-key","dd-plugin","moodle-core-widget-focusafterclose","moodle-core-lockscroll"]});
diff --git a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
index 77ad4e495de..26caaf2a363 100644
--- a/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
+++ b/lib/yui/build/moodle-core-notification-dialogue/moodle-core-notification-dialogue.js
@@ -331,6 +331,11 @@ Y.extend(DIALOGUE, Y.Panel, {
                                 'height' : this.get('height')});
             }
         }
+
+        // Update Lock scroll if the plugin is present.
+        if (this.lockScroll) {
+            this.lockScroll.updateScrollLock(this.shouldResizeFullscreen());
+        }
     },
     /**
      * Center the dialog on the screen.
@@ -387,13 +392,6 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.get('boundingBox').setXY(this._originalPosition);
         }
 
-        // Lock scroll if the plugin is present.
-        if (this.lockScroll) {
-            // We need to force the scroll locking for full screen dialogues, even if they have a small vertical size to
-            // prevent the background scrolling while the dialogue is open.
-            this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
-        }
-
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);
diff --git a/lib/yui/src/lockscroll/js/lockscroll.js b/lib/yui/src/lockscroll/js/lockscroll.js
index c9487fbd124..226b30f4ee4 100644
--- a/lib/yui/src/lockscroll/js/lockscroll.js
+++ b/lib/yui/src/lockscroll/js/lockscroll.js
@@ -55,12 +55,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             return;
         }
 
-        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
-            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
-            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
-            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
-
-        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+        if (!this.shouldLockScroll(forceOnSmallWindow)) {
             Y.log('Dialogue height greater than window height. Ignoring enable request.', 'warn', 'moodle-core-lockscroll');
             return;
         }
@@ -94,6 +89,44 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
         return this;
     },
 
+    /**
+     * Recalculate whether lock scrolling should be on or off.
+     *
+     * @method shouldLockScroll
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @return boolean
+     */
+    shouldLockScroll: function(forceOnSmallWindow) {
+        var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
+            // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
+            // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
+            windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
+
+        if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
+            return false;
+        } else {
+            return true;
+        }
+    },
+
+    /**
+     * Recalculate whether lock scrolling should be on or off because the size of the dialogue changed.
+     *
+     * @method updateScrollLock
+     * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
+     * @chainable
+     */
+    updateScrollLock: function(forceOnSmallWindow) {
+        // Both these functions already check if scroll lock is active and do the right thing.
+        if (this.shouldLockScroll(forceOnSmallWindow)) {
+            this.enableScrollLock(forceOnSmallWindow);
+        } else {
+            this.disableScrollLock(true);
+        }
+
+        return this;
+    },
+
     /**
      * Stop locking the page scroll.
      *
@@ -103,7 +136,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
      * @method disableScrollLock
      * @chainable
      */
-    disableScrollLock: function() {
+    disableScrollLock: function(force) {
         if (this.isActive()) {
             Y.log('Disabling LockScroll.', 'debug', 'moodle-core-lockscroll');
             this._enabled = false;
@@ -115,7 +148,7 @@ Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, []
             var currentCount = parseInt(body.getAttribute('data-activeScrollLocks'), 10) || 1,
                 newCount = currentCount - 1;
 
-            if (currentCount === 1) {
+            if (force || currentCount === 1) {
                 body.removeClass('lockscroll');
                 body.setStyle('maxWidth', null);
             }
diff --git a/lib/yui/src/notification/js/dialogue.js b/lib/yui/src/notification/js/dialogue.js
index c1cbbf0bd27..8f0220c7d2d 100644
--- a/lib/yui/src/notification/js/dialogue.js
+++ b/lib/yui/src/notification/js/dialogue.js
@@ -302,6 +302,11 @@ Y.extend(DIALOGUE, Y.Panel, {
                                 'height' : this.get('height')});
             }
         }
+
+        // Update Lock scroll if the plugin is present.
+        if (this.lockScroll) {
+            this.lockScroll.updateScrollLock(this.shouldResizeFullscreen());
+        }
     },
     /**
      * Center the dialog on the screen.
@@ -358,13 +363,6 @@ Y.extend(DIALOGUE, Y.Panel, {
             this.get('boundingBox').setXY(this._originalPosition);
         }
 
-        // Lock scroll if the plugin is present.
-        if (this.lockScroll) {
-            // We need to force the scroll locking for full screen dialogues, even if they have a small vertical size to
-            // prevent the background scrolling while the dialogue is open.
-            this.lockScroll.enableScrollLock(this.shouldResizeFullscreen());
-        }
-
         // Try and find a node to focus on using the focusOnShowSelector attribute.
         if (focusSelector !== null) {
             focusNode = this.get('boundingBox').one(focusSelector);