Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.76
diff -u -r1.76 form.inc
--- includes/form.inc	9 Mar 2006 22:55:01 -0000	1.76
+++ includes/form.inc	12 Mar 2006 02:55:43 -0000
@@ -331,6 +331,10 @@
           $form['#value'] = '0'; // checkbox unchecked
           $form['#needs_validation'] = TRUE;
         }
+        elseif (isset($form['#default_value'])) {
+          $form['#value'] = array(); // empty multiple-select element
+          $form['#needs_validation'] = TRUE;
+        }
       }
       if (!isset($form['#value'])) {
         $function = $form['#type'] . '_value';