Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.502
diff -u -p -r1.502 form.inc
--- includes/form.inc	7 Oct 2010 17:31:39 -0000	1.502
+++ includes/form.inc	12 Oct 2010 17:14:01 -0000
@@ -1982,32 +1982,14 @@ function form_state_values_clean(&$form_
   // form_builder() collects all button elements in a form. We remove the button
   // value separately for each button element.
   foreach ($form_state['buttons'] as $button) {
-    // Remove this button's value from the submitted form values by finding
-    // the value corresponding to this button.
-    // We iterate over the #parents of this button and move a reference to
-    // each parent in $form_state['values']. For example, if #parents is:
-    //   array('foo', 'bar', 'baz')
-    // then the corresponding $form_state['values'] part will look like this:
-    // array(
-    //   'foo' => array(
-    //     'bar' => array(
-    //       'baz' => 'button_value',
-    //     ),
-    //   ),
-    // )
-    // We start by (re)moving 'baz' to $last_parent, so we are able unset it
-    // at the end of the iteration. Initially, $values will contain a
-    // reference to $form_state['values'], but in the iteration we move the
-    // reference to $form_state['values']['foo'], and finally to
-    // $form_state['values']['foo']['bar'], which is the level where we can
-    // unset 'baz' (that is stored in $last_parent).
-    $parents = $button['#parents'];
     $values = &$form_state['values'];
+    $parents = $button['#parents'];
     $last_parent = array_pop($parents);
-    foreach ($parents as $parent) {
-      $values = &$values[$parent];
+    $key_exists = NULL;
+    drupal_array_get_nested_value($values, $parents, $key_exists);
+    if ($key_exists) {
+      unset($values[$last_parent]);
     }
-    unset($values[$last_parent]);
   }
 }