--- book.orig.module	2007-03-18 01:16:52.000000000 +0000
+++ book.module	2007-03-18 01:16:53.000000000 +0000
@@ -443,7 +443,7 @@
       }
       break;
     case 'update':
-      if (isset($node->parent)) {
+      if (isset($node->parent) && $node->type == 'book') {
         if (!empty($node->revision)) {
           db_query("INSERT INTO {book} (nid, vid, parent, weight) VALUES (%d, %d, %d, %d)", $node->nid, $node->vid, $node->parent, $node->weight);
         }