Index: modules/forum/forum.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/forum/forum.module,v
retrieving revision 1.427
diff -u -r1.427 forum.module
--- modules/forum/forum.module	21 Nov 2007 09:31:57 -0000	1.427
+++ modules/forum/forum.module	21 Nov 2007 11:21:49 -0000
@@ -361,6 +361,10 @@
       $form['settings']['required'] = array('#type' => 'value', '#value' => 1);
     }
   }
+  // Hide multiple parents select from forum terms.
+  if ($form_id == 'taxonomy_form_term') {
+    unset($form['advanced']['parent']);
+  }
 }
 
 /**