Index: form.inc
===================================================================
--- form.inc	(revision 3708)
+++ form.inc	(working copy)
@@ -574,9 +574,7 @@
  *   not be repeated in the submission step.
  */
 function drupal_validate_form($form_id, $form, &$form_state) {
-  static $validated_forms = array();
-
-  if (isset($validated_forms[$form_id])) {
+  if (isset($form_state['drupal_validate_form_already'])) {
     return;
   }

@@ -590,7 +588,7 @@
   }

   _form_validate($form, $form_state, $form_id);
-  $validated_forms[$form_id] = TRUE;
+  $form_state['drupal_validate_form_already'] = TRUE;
 }

 /**