Index: wp-includes/kses.php
===================================================================
--- wp-includes/kses.php	(revision 18392)
+++ wp-includes/kses.php	(working copy)
@@ -403,6 +403,7 @@
 	$allowedtags = array(
 		'a' => array(
 			'href' => array (),
+			'rel' => array (),
 			'title' => array ()),
 		'abbr' => array(
 			'title' => array ()),