Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.323
diff -u -p -r1.323 system.admin.inc
--- modules/system/system.admin.inc	20 Oct 2010 16:19:24 -0000	1.323
+++ modules/system/system.admin.inc	25 Oct 2010 05:10:59 -0000
@@ -350,6 +350,13 @@ function system_theme_default() {
       }
       // Set the default theme.
       variable_set('theme_default', $theme);
+
+      // Rebuild the menu. This duplicates the menu_rebuild() in theme_enable()
+      // however modules must know the current default theme in order to use
+      // this information in hook_menu() or hook_menu_alter() implementations.
+      // And doing the variable_set() before the theme_enable() could result
+      // in a race condition where the theme is default but not enabled.
+      menu_rebuild();
       // The status message depends on whether an admin theme is currently in use:
       // a value of 0 means the admin theme is set to be the default theme.
       $admin_theme = variable_get('admin_theme', 0);