To me the fact that you can get a different hash for http://weblearn.ox.ac.uk/access/site/content.pdf and /access/site/content.pdf is a bug in the URL shortening service.

The protocol/hostname are superfluous and make it harder to test anything on a server other than the live server. If content has links such as <a href="/access/site/content.pdf">My Content</a> then they work on staging as well.