Solved a problem where the '1' string was being cached to ''

because we concatenate true and it's evaluated like 1.
Bug 3623.
(http://moodle.org/bugs/bug.php?op=show&bugid=3623)

lib/weblib.php

@@ -1155,7 +1155,7 @@ function format_string ($string, $striplinks = false, $courseid=NULL ) {
     static $strcache;
 
     //Calculate md5
-    $md5 = md5($string.$striplinks);
+    $md5 = md5($string.'<+>'.$striplinks);
 
     //Fetch from cache if possible
     if(isset($strcache[$md5])) {