MDL-9114: Resolved the issue for the most part. However still a problem when jumping from a group with users to an empty group. If you do so too quickly, the empty group shows the members of the previously highlighted group. But there is no more accumulation of users from one group to the next.

group/lib/clientlib.js

@@ -116,10 +116,15 @@ function UpdatableMembersCombo(wwwRoot, courseId) {
 
         	if (o.responseText !== undefined) {
                 var selectEl = document.getElementById("members");
-
         	    if (selectEl && o.responseText) {
         	        var members = eval("("+o.responseText+")");
 
+                    // Clear the members combo box.
+                    if (selectEl) {
+                        while (selectEl.firstChild) {
+                            selectEl.removeChild(selectEl.firstChild);
+                        }
+                    }
         	        // Populate the members combo box.
                     for (var i=0; i<members.length; i++) {
                         var optionEl = document.createElement("option");
@@ -151,9 +156,9 @@ function UpdatableMembersCombo(wwwRoot, courseId) {
 UpdatableMembersCombo.prototype.refreshMembers = function (groupId) {
     // Add the loader gif image.
     createLoaderImg("membersloader", "memberslabel", this.wwwRoot);
+    var selectEl = document.getElementById("members");
 
     // Clear the members combo box.
-    var selectEl = document.getElementById("members");
     if (selectEl) {
         while (selectEl.firstChild) {
             selectEl.removeChild(selectEl.firstChild);
@@ -164,7 +169,7 @@ UpdatableMembersCombo.prototype.refreshMembers = function (groupId) {
     document.getElementById("showeditgroupsettingsform").disabled = false;
     document.getElementById("deletegroup").disabled = false;
     var sUrl = this.wwwRoot+"/group/index.php?id="+this.courseId+"&group="+groupId+"&act_ajax_getmembersingroup";
-    YAHOO.util.Connect.asyncRequest("GET", sUrl, this.connectCallback, null);
+    YAHOO.util.Connect.asyncRequest("GET", sUrl, this.connectCallback, null); 
 };