diff --git a/lib/db/caches.php b/lib/db/caches.php
index ffb2877d495..347c824c53b 100644
--- a/lib/db/caches.php
+++ b/lib/db/caches.php
@@ -81,6 +81,7 @@ $definitions = array(
     // This caches the html purifier cleaned text. This is done because the text is usually cleaned once for every user
     // and context combo. Text caching handles caching for the combination, this cache is responsible for caching the
     // cleaned text which is shareable.
+    // NOTE: this data may be safely stored in local caches on cluster nodes.
     'htmlpurifier' => array(
         'mode' => cache_store::MODE_APPLICATION,
     ),
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index c190a823f93..0f2f3fb3f9c 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -1596,10 +1596,6 @@ function purge_all_caches() {
     // Make sure cache dir is writable, throws exception if not.
     make_cache_directory('');
 
-    // Hack: this script may get called after the purifier was initialised,
-    // but we do not want to verify repeatedly this exists in each call.
-    make_cache_directory('htmlpurifier');
-
     // This is the only place where we purge local caches, we are only adding files there.
     // The $CFG->localcachedirpurged flag forces local directories to be purged on cluster nodes.
     remove_dir($CFG->localcachedir, true);
diff --git a/lib/testing/classes/util.php b/lib/testing/classes/util.php
index 4dfa12c4cb6..5cef5ea5ba0 100644
--- a/lib/testing/classes/util.php
+++ b/lib/testing/classes/util.php
@@ -598,7 +598,6 @@ abstract class testing_util {
         closedir($handle);
         make_temp_directory('');
         make_cache_directory('');
-        make_cache_directory('htmlpurifier');
         make_localcache_directory('');
         // Reset the cache API so that it recreates it's required directories as well.
         cache_factory::reset();
diff --git a/lib/tests/htmlpurifier_test.php b/lib/tests/htmlpurifier_test.php
index 3e803d9601f..88a16440ae1 100644
--- a/lib/tests/htmlpurifier_test.php
+++ b/lib/tests/htmlpurifier_test.php
@@ -124,6 +124,37 @@ class core_htmlpurifier_testcase extends basic_testcase {
         $this->assertSame('<div id="example">Frog</div>', $result);
     }
 
+    public function test_allowobjectembed() {
+        global $CFG;
+
+        $this->assertSame('0', $CFG->allowobjectembed);
+
+        $text = '<object width="425" height="350">
+<param name="movie" value="http://www.youtube.com/v/AyPzM5WK8ys" />
+<param name="wmode" value="transparent" />
+<embed src="http://www.youtube.com/v/AyPzM5WK8ys" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350" />
+</object>hmmm';
+        $result = purify_html($text, array());
+        $this->assertSame('hmmm', trim($result));
+
+        $CFG->allowobjectembed = '1';
+
+        $expected = '<object width="425" height="350" data="http://www.youtube.com/v/AyPzM5WK8ys" type="application/x-shockwave-flash">
+<param name="allowScriptAccess" value="never" />
+<param name="allowNetworking" value="internal" />
+<param name="movie" value="http://www.youtube.com/v/AyPzM5WK8ys" />
+<param name="wmode" value="transparent" />
+<embed src="http://www.youtube.com/v/AyPzM5WK8ys" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350" allowscriptaccess="never" allownetworking="internal" />
+</object>hmmm';
+        $result = purify_html($text, array());
+        $this->assertSame(str_replace("\n", '', $expected), str_replace("\n", '', $result));
+
+        $CFG->allowobjectembed = '0';
+
+        $result = purify_html($text, array());
+        $this->assertSame('hmmm', trim($result));
+    }
+
     /**
      * Test if linebreaks kept unchanged.
      */
diff --git a/lib/weblib.php b/lib/weblib.php
index c9b617574f1..43e58092ea2 100644
--- a/lib/weblib.php
+++ b/lib/weblib.php
@@ -1615,27 +1615,47 @@ function is_purify_html_necessary($text) {
 function purify_html($text, $options = array()) {
     global $CFG;
 
+    $text = (string)$text;
+
     static $purifiers = array();
     static $caches = array();
 
-    $type = !empty($options['allowid']) ? 'allowid' : 'normal';
+    // Purifier code can change only during major version upgrade.
+    $version = empty($CFG->version) ? 0 : $CFG->version;
+    $cachedir = "$CFG->localcachedir/htmlpurifier/$version";
+    if (!file_exists($cachedir)) {
+        // Purging of caches may remove the cache dir at any time,
+        // luckily file_exists() results should be cached for all existing directories.
+        $purifiers = array();
+        $caches = array();
+        gc_collect_cycles();
+
+        make_localcache_directory('htmlpurifier', false);
+        check_dir_exists($cachedir);
+    }
+
+    $allowid = empty($options['allowid']) ? 0 : 1;
+    $allowobjectembed = empty($CFG->allowobjectembed) ? 0 : 1;
+
+    $type = 'type_'.$allowid.'_'.$allowobjectembed;
 
     if (!array_key_exists($type, $caches)) {
         $caches[$type] = cache::make('core', 'htmlpurifier', array('type' => $type));
     }
     $cache = $caches[$type];
 
-    $filteredtext = $cache->get($text);
-    if ($filteredtext !== false) {
+    // Add revision number and all options to the text key so that it is compatible with local cluster node caches.
+    $key = "|$version|$allowobjectembed|$allowid|$text";
+    $filteredtext = $cache->get($key);
+
+    if ($filteredtext === true) {
+        // The filtering did not change the text last time, no need to filter anything again.
+        return $text;
+    } else if ($filteredtext !== false) {
         return $filteredtext;
     }
 
     if (empty($purifiers[$type])) {
-
-        // make sure the serializer dir exists, it should be fine if it disappears later during cache reset
-        $cachedir = $CFG->cachedir.'/htmlpurifier';
-        check_dir_exists($cachedir);
-
         require_once $CFG->libdir.'/htmlpurifier/HTMLPurifier.safe-includes.php';
         require_once $CFG->libdir.'/htmlpurifier/locallib.php';
         $config = HTMLPurifier_Config::createDefault();
@@ -1651,22 +1671,22 @@ function purify_html($text, $options = array()) {
         $config->set('URI.AllowedSchemes', array('http'=>true, 'https'=>true, 'ftp'=>true, 'irc'=>true, 'nntp'=>true, 'news'=>true, 'rtsp'=>true, 'teamspeak'=>true, 'gopher'=>true, 'mms'=>true, 'mailto'=>true));
         $config->set('Attr.AllowedFrameTargets', array('_blank'));
 
-        if (!empty($CFG->allowobjectembed)) {
+        if ($allowobjectembed) {
             $config->set('HTML.SafeObject', true);
             $config->set('Output.FlashCompat', true);
             $config->set('HTML.SafeEmbed', true);
         }
 
-        if ($type === 'allowid') {
+        if ($allowid) {
             $config->set('Attr.EnableID', true);
         }
 
         if ($def = $config->maybeGetRawHTMLDefinition()) {
-            $def->addElement('nolink', 'Block', 'Flow', array());                       // skip our filters inside
-            $def->addElement('tex', 'Inline', 'Inline', array());                       // tex syntax, equivalent to $$xx$$
-            $def->addElement('algebra', 'Inline', 'Inline', array());                   // algebra syntax, equivalent to @@xx@@
-            $def->addElement('lang', 'Block', 'Flow', array(), array('lang'=>'CDATA')); // old and future style multilang - only our hacked lang attribute
-            $def->addAttribute('span', 'xxxlang', 'CDATA');                             // current problematic multilang
+            $def->addElement('nolink', 'Block', 'Flow', array());                       // Skip our filters inside.
+            $def->addElement('tex', 'Inline', 'Inline', array());                       // Tex syntax, equivalent to $$xx$$.
+            $def->addElement('algebra', 'Inline', 'Inline', array());                   // Algebra syntax, equivalent to @@xx@@.
+            $def->addElement('lang', 'Block', 'Flow', array(), array('lang'=>'CDATA')); // Original multilang style - only our hacked lang attribute.
+            $def->addAttribute('span', 'xxxlang', 'CDATA');                             // Current very problematic multilang.
         }
 
         $purifier = new HTMLPurifier($config);
@@ -1681,11 +1701,18 @@ function purify_html($text, $options = array()) {
     if ($multilang) {
         $filteredtext = preg_replace('/<span(\s+lang="([a-zA-Z0-9_-]+)"|\s+class="multilang"){2}\s*>/', '<span xxxlang="${2}">', $filteredtext);
     }
-    $filteredtext = $purifier->purify($filteredtext);
+    $filteredtext = (string)$purifier->purify($filteredtext);
     if ($multilang) {
         $filteredtext = preg_replace('/<span xxxlang="([a-zA-Z0-9_-]+)">/', '<span lang="${1}" class="multilang">', $filteredtext);
     }
-    $cache->set($text, $filteredtext);
+
+    if ($text === $filteredtext) {
+        // No need to store the filtered text, next time we will just return unfiltered text
+        // because it was not changed by purifying.
+        $cache->set($key, true);
+    } else {
+        $cache->set($key, $filteredtext);
+    }
 
     return $filteredtext;
 }