--- modules/forum/forum.module	2010-08-30 15:47:29.000000000 -0400
+++ modules/forum/forum.module	2010-08-30 15:48:16.000000000 -0400
@@ -255,7 +255,7 @@
             $node->tid = $term_id;
           }
         }
-        $old_tid = db_result(db_query_range("SELECT t.tid FROM {term_node} t INNER JOIN {node} n ON t.vid = n.vid WHERE n.nid = %d ORDER BY t.vid DESC", $node->nid, 0, 1));
+        $old_tid = db_result(db_query_range("SELECT f.tid FROM {forum} f INNER JOIN {node} n ON f.vid = n.vid WHERE n.nid = %d ORDER BY f.vid DESC", $node->nid, 0, 1));
         if ($old_tid && isset($node->tid) && ($node->tid != $old_tid) && !empty($node->shadow)) {
           // A shadow copy needs to be created. Retain new term and add old term.
           $node->taxonomy[] = $old_tid;