only in patch2:
unchanged:
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -971,7 +971,7 @@ function theme($hook, $variables = array()) {
     $variables = array();
     if (isset($info['variables'])) {
       foreach (array_keys($info['variables']) as $name) {
-        if (isset($element["#$name"])) {
+        if (array_key_exists("#$name", $element)) {
           $variables[$name] = $element["#$name"];
         }
       }