--- formatting.php.ori	2011-06-27 15:56:42.000000000 +0200
+++ formatting.php	2011-09-24 18:02:00.502741800 +0200
@@ -2372,7 +2372,7 @@
  * @return string
  */
 function tag_escape($tag_name) {
-	$safe_tag = strtolower( preg_replace('/[^a-zA-Z_:]/', '', $tag_name) );
+	$safe_tag = strtolower( preg_replace('/[^a-zA-Z0-9_:]/', '', $tag_name) );
 	return apply_filters('tag_escape', $safe_tag, $tag_name);
 }