Index: wp-includes/kses.php
===================================================================
--- wp-includes/kses.php	(revision 3332)
+++ wp-includes/kses.php	(working copy)
@@ -98,6 +98,10 @@
 		return '>';
 	# It matched a ">" character
 
+	if (preg_match('%^<!--[^>-]+-->$%', $string))
+		return $string;
+	# Allow HTML comments
+
 	if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $string, $matches))
 		return '';
 	# It's seriously malformed