- Patch #221057 by pwolanin: book module may overwrite another node's link.

modules/book/book.module

@@ -683,6 +683,10 @@ function book_nodeapi(&$node, $op, $teaser, $page) {
       if (!empty($node->book['bid']) && !user_access('administer nodes')) {
         $node->revision = 1;
       }
+      // Make sure a new node gets a new menu link.
+      if (empty($node->nid)) {
+        $node->book['mlid'] = NULL;
+      }
       break;
     case 'insert':
     case 'update':