--- includes/theme.inc	2009-02-22 12:55:29.000000000 -0500
+++ includes/themeNew.inc	2009-03-25 19:58:31.000000000 -0400
@@ -605,6 +605,8 @@ function theme() {
   }
 
   if (!isset($hooks[$hook])) {
+    $msg = t("Cannot locate '@hook()' in theme registry", array('@hook' => 'theme_' . $hook));
+    watchdog('theme', $msg, array(), WATCHDOG_WARNING);
     return;
   }