Index: trunk/roundcubemail/program/include/rcube_imap.php
===================================================================
--- trunk/roundcubemail/program/include/rcube_imap.php	(revision 4741)
+++ trunk/roundcubemail/program/include/rcube_imap.php	(revision 4743)
@@ -3050,8 +3050,10 @@
     private function _list_mailboxes($root='', $name='*', $filter=null)
     {
-        $cache_key = 'mailboxes';
+        $cache_key = $root.':'.$name;
         if (!empty($filter)) {
-            $cache_key .= '.'.substr((is_string($filter) ? $filter : serialize($filter)), 0, 90);
-        }
+            $cache_key .= ':'.(is_string($filter) ? $filter : serialize($filter));
+        }
+
+        $cache_key = 'mailboxes.'.md5($cache_key);
 
         // get cached folder list