Index: includes/theme.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.inc,v
retrieving revision 1.500
diff -u -p -r1.500 theme.inc
--- includes/theme.inc	27 Jul 2009 18:38:35 -0000	1.500
+++ includes/theme.inc	28 Jul 2009 21:18:02 -0000
@@ -696,6 +696,7 @@ function theme() {
 
   if (is_array($hook)) {
     foreach ($hook as $candidate) {
+      $candidate = strtolower($candidate);
       if (isset($hooks[$candidate])) {
         break;
       }