Index: modules/user/user.pages.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.pages.inc,v
retrieving revision 1.11.2.2
diff -u -F '^f' -r1.11.2.2 user.pages.inc
--- modules/user/user.pages.inc	16 Sep 2009 17:54:20 -0000	1.11.2.2
+++ modules/user/user.pages.inc	1 Jan 2010 03:41:58 -0000
@@ -151,6 +151,7 @@ function user_logout() {
   // Only variables can be passed by reference workaround.
   $null = NULL;
   user_module_invoke('logout', $null, $user);
+  $_SESSION = array();
 
   // Load the anonymous user
   $user = drupal_anonymous_user();