Index: wp-includes/theme.php
===================================================================
--- wp-includes/theme.php	(revision 11521)
+++ wp-includes/theme.php	(working copy)
@@ -1153,7 +1153,7 @@
 	$file = preg_replace('|/+|','/', $file); // remove any duplicate slash
 	$theme_dir = str_replace('\\','/', get_theme_root()); // sanitize for Win32 installs
 	$theme_dir = preg_replace('|/+|','/', $theme_dir); // remove any duplicate slash
-	$file = preg_replace('|^.*/themes/.*?/|','',$file); // get relative path from theme dir
+	$file = preg_replace('|^'. preg_quote($theme_dir, '#') .'/|','',$file); // get relative path from theme dir
 	return $file;
 }