#305653 follow-up by sun: Prevent themes from being disabled during update.

includes/common.inc

@@ -3950,7 +3950,16 @@ function drupal_flush_all_caches() {
   registry_rebuild();
   drupal_clear_css_cache();
   drupal_clear_js_cache();
-  system_theme_data();
+
+  // If invoked from update.php, we must not update the theme information in the
+  // database, or this will result in all themes being disabled.
+  if (defined('MAINTENANCE_MODE') && MAINTENANCE_MODE == 'update') {
+    _system_theme_data();
+  }
+  else {
+    system_theme_data();
+  }
+
   drupal_theme_rebuild();
   menu_rebuild();
   node_types_rebuild();