Index: forum.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/forum.module,v
retrieving revision 1.260
diff -u -Ffunction -r1.260 forum.module
--- forum.module	1 Aug 2005 05:14:05 -0000	1.260
+++ forum.module	18 Aug 2005 15:55:30 -0000
@@ -134,6 +134,9 @@ function forum_taxonomy($op, $type, $obj
       node_delete($edit);
     }
   }
+  elseif ($op == 'delete' && $type == 'vocabulary' && $object->vid == _forum_get_vid())  {
+    variable_del('forum_nav_vocabulary');
+  }
 }
 
 /**