I accidently looked up this release, but actually the guid is a release-group
http://test.musicbrainz.org/ws/2/release/cbf7472a-725d-3904-b0c4-2a73e4a8dfa2

It just returns nothing at all, it should either return an error similar to the current musicbrainz server

http://musicbrainz.org/ws/1/release/cbf7472a-725d-3904-b0c4-2a73e4a8dfa2?type=xml

or an empty list such as:

<?xml version="1.0" encoding="UTF-8"?>
<metadata xmlns="http://musicbrainz.org/ns/mmd-2.0#">
</metadata