Compare http://test.musicbrainz.org/release-group/6b4bc5d7-4ea3-44da-9e44-a3163432939d and http://test.musicbrainz.org/release-group/6b4bc5d7-4ea3-44da-9e44-a3163432939d/set-cover-art
The former lists the releases as I would expect. The latter lists them in what I can only imagine is a random order, since they're not even sorted by date.