path alias work problem

Hello.

I'm working on one module with self-made nodes involved. I was using pathauto to create path aliases like "nodetype/nodetitle" for every of my nodes for a while. But then I had to create more aliases for every node, like "nodetype/nodetitle/operation". So I decided to remove pathauto and create all those aliases with path_set_alias function.

The task itself is pretty simple: to add aliases at node creation, to modify them at node update and to delete at node removal. So I added a couple of path_set_alias calls at hook_insert - and failed. Aliases at path_set_alias("node/".$nid."/operation",$aliasname) were set fine, but there was no way to set aliases like path_set_alias("node/".$nid,"something/title"). Function just didn't add anything to {url_alias} table.

Eventually I figured to move my path_set_alias calls to hook_nodeapi, something like:

	if (($op == 'presave') && ($node->type == 'mytype')) {
		$node->path = NULL; //to avoid probable conflict with path_nodeapi
	}
	if ((($op == 'insert') || ($op == 'update')) && ($node->type == 'mytype')) {
		//delete aliases if any
		path_set_alias("node/".$node->nid);
		path_set_alias("node/".$node->nid."/operation");
		//create new aliases
		path_set_alias("node/".$node->nid,"mytype/".$alias_name);
		path_set_alias("node/".$node->nid."/operation","mytype/".$alias_name."/operation");
	}

and it seems to work fine :)

Anyway I don't get why I can't create path alias for node page at hook_insert. It's not really a problem since I figured a workaround above, but I would really like to understand how it works. Any ideas?

Thank you.