Why no pid in node object? I am setting an alias programatically, using path_set_alias() in Drupal6.

Looking at the code of path_set_alias in path.module, I see that if I pass the pid (path id), the old alias(s) for that node will get deleted, which is what I want.

When I load the node, though, I see no pid property set on the node, but the record for the node's alias exists in url_alias table.

Why doesn't pid exist on the node object? Must I retrieve the pid from the url_alias table and then pass that in to path_set_alias to remove the old alias?
It looks like a bug, see http://drupal.org/node/633916

It's optional to path the pid to path_set_alias() so it should work without passing it.