Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 4444)
+++ /CKEditor/trunk/CHANGES.html	(revision 4445)
@@ -50,4 +50,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/4401">#4401</a> : Fixed customized by removing 'upload' tab page from 'Link dialog' cause JavaScript error.</li>
 		<li><a href="http://dev.fckeditor.net/ticket/4477">#4477</a> : Adding missing tag names in object style elements.</li>
+		<li><a href="http://dev.fckeditor.net/ticket/4567">#4567</a> : Fixed IE throw error when pressing 'Back Space' in source mode.</li>
 	</ul>
 	<h3>
Index: /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 4444)
+++ /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 4445)
@@ -460,4 +460,7 @@
 							editor.on( 'key', function( event )
 							{
+								if( editor.mode != 'wysiwyg' )
+									return;
+
 								// Backspace.
 								var control = event.data.keyCode == 8