unexpected update of book table in nodeapi update

Say a module uses it's own node hierarchy (like acidfree, tasklist). They have the parent field in their own table, and implement as a result this field in the node object: $node->parent
The problem is when they use the node_save function for updating a node.
Here is the pipeline:
* node_save($node); //mymodule.module
* node_invoke_nodeapi($node, 'update'); //node.module
* book_nodeapi($node, 'update'); //book.module

Here is the detail of what happens in the book nodeapi update

    case 'update':
      if (isset($node->parent)) {
        if ($node->revision) {
          db_query("INSERT INTO {book} (nid, vid, parent, weight) VALUES (%d, %d, %d, %d)", $node->nid, $node->vid, $node->parent, $node->weight);
        }
        else {
          db_query("UPDATE {book} SET parent = %d, weight = %d WHERE vid = %d", $node->parent, $node->weight, $node->vid);
        }
      }
      break;

because the $node->parent is present in this node, this node is treated as a book page. The test should not be only if (isset($node->parent)) but if (isset($node->parent) && $node->type == 'book').
I think the modules should keep their own hierarchy in their own tables, if not, the book table should be renamed node_hierarchy. It becomes quite confusing otherwise.

The visible effect of this is that every nodes I edit appear at the bottom of the parent node such as a book. I posted an issue with more details in the tasklist project.
The patch is against the book.module file // $Id: book.module,v 1.412 2007/03/17 18:30:14 dries Exp $