Sometimes creating bad node hierarchy

I have a custom code to create a wiki type node when i create an og type node (with hook_nodeapi -> insert).
When i create a node hierarchy with an og node as a child, the Node Hierarchy module creates a relation with the wiki node too.

So, to solve the problem, i added a verification in node_hierarchy_insert_node to see if $node->parent is defined :
if ($node->nid && isset($node->parent) && (($node->old_parent !== $node->parent) || $node->old_parent === NULL))
instead of
if ($node->nid && (($node->old_parent !== $node->parent) || $node->old_parent === NULL))

Thanks,

--
Samuel