Index: wp-admin/edit-form-advanced.php
===================================================================
--- wp-admin/edit-form-advanced.php	(revision 22780)
+++ wp-admin/edit-form-advanced.php	(working copy)
@@ -423,14 +423,26 @@
 <script type="text/javascript">
 (function($){
 	function getFieldsContent() {
-		return ($('#title').val() || '') + ($('#attachment_caption').val() || '') +
-		($('#attachment_alt').val() || '') + ($('#attachment_content').val() || '') + ($('#post_name').val() || '');
+		return [ $('#title').val() || '',
+			$('#attachment_caption').val() || '',
+			$('#attachment_alt').val() || '',
+			$('#attachment_content').val() || '',
+			$('#post_name').val() || '' ];
 	}
 
 	var initial = getFieldsContent();
 
 	window.onbeforeunload = function() {
-		if ( initial != getFieldsContent() )
+		var changed;
+
+		$.each( getFieldsContent(), function(i, field) {
+			if ( field != initial[i] ) {
+				changed = true;
+				return;
+			}
+		});
+
+		if ( changed )
 			return '<?php _e('The changes you made will be lost if you navigate away from this page.'); ?>';
 	};
 })(jQuery);