Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 17446)
+++ wp-includes/formatting.php	(working copy)
@@ -692,7 +692,7 @@
  */
 function sanitize_file_name( $filename ) {
 	$filename_raw = $filename;
-	$special_chars = array("?", "[", "]", "/", "\\", "=", "<", ">", ":", ";", ",", "'", "\"", "&", "$", "#", "*", "(", ")", "|", "~", "`", "!", "{", "}", chr(0));
+	$special_chars = array("?", "[", "]", "/", "\\", "=", "<", ">", ":", ";", ",", "'", "\"", "&", "$", "#", "*", "(", ")", "|", "~", "`", "!", "{", "}", '%', chr(0));
 	$special_chars = apply_filters('sanitize_file_name_chars', $special_chars, $filename_raw);
 	$filename = str_replace($special_chars, '', $filename);
 	$filename = preg_replace('/[\s-]+/', '-', $filename);