Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 3789)
+++ /CKEditor/trunk/CHANGES.html	(revision 3790)
@@ -80,4 +80,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/3730">#3730</a> : Indent is performing on the whole
 			block instead of selected lines in enterMode = BR.</li>
+		<li><a href="http://dev.fckeditor.net/ticket/3844">#3844</a> : Fixed UndoManager register keydown on obsoleted document</li>
 	</ul>
 	<h3>
Index: /CKEditor/trunk/_source/plugins/undo/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/undo/plugin.js	(revision 3789)
+++ /CKEditor/trunk/_source/plugins/undo/plugin.js	(revision 3790)
@@ -70,4 +70,16 @@
 				});
 
+			// Registering keydown on every document recreation.(#3844)
+			editor.on( 'contentDom', function()
+			{
+				editor.document.on( 'keydown', function( event )
+					{
+						// Do not capture CTRL hotkeys.
+						if ( !event.data.$.ctrlKey && !event.data.$.metaKey )
+							undoManager.type( event );
+					});
+
+			} );
+
 			// Make the undo manager available only in wysiwyg mode.
 			editor.on( 'mode', function()
@@ -78,12 +90,4 @@
 						{
 							undoManager.enabled = true;
-
-							editor.document.on( 'keydown', function( event )
-								{
-									// Do not capture CTRL hotkeys.
-									if ( !event.data.$.ctrlKey && !event.data.$.metaKey )
-										undoManager.type( event );
-								});
-
 							// Always save an undo snapshot - the previous mode might have changed
 							// editor contents.