Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.904
diff -u -p -r1.904 system.module
--- modules/system/system.module	21 Mar 2010 21:20:43 -0000	1.904
+++ modules/system/system.module	22 Mar 2010 02:29:01 -0000
@@ -2704,7 +2704,7 @@ function system_admin_compact_mode() {
  */
 function system_admin_compact_page($mode = 'off') {
   global $user;
-  user_save($user, array('admin_compact_mode' => ($mode == 'on')));
+  user_save($user, array('data' => array('admin_compact_mode' => ($mode == 'on'))));
   drupal_goto();
 }