--- modules/user/user.pages.inc.orig	2010-03-23 13:15:13.000000000 -0400
+++ modules/user/user.pages.inc	2010-03-23 13:12:34.000000000 -0400
@@ -152,6 +152,7 @@ function user_logout() {
 
   // Destroy the current session, and reset $user to the anonymous user.
   session_destroy();
+  $_SESSION = array();
 
   // Load the anonymous user
   $user = drupal_anonymous_user();