There are two cases:
1. Page object is not loaded before plugin
It will add this to Github if it’s missing, as you suggested.
http://forum.getkirby.com/t/functions-unable-to-load-the-page-object/1081
2. $page->url() is wrong when routed
When in a template and try this on a routed page it’s not correct:
echo $page->url();
It returns the original uri, not the routed one.