Switching both my CD ripper and my ISRC submitter to use test.musicbrainz.org breaks both of them. Both can retrieve the same disc from musicbrainz.org with no problems.

Looking at http://musicbrainz.org/ws/1/release/?type=xml&discid=p8f2NrIeNd6fWFCGP_yVLTuZRwg- and http://test.musicbrainz.org/ws/1/release/?type=xml&discid=p8f2NrIeNd6fWFCGP_yVLTuZRwg- they're not the same. mb.org has <release-list><release> and <disc-list count="1"/> whereas test.mb.org has <release><release> and <disc-list count="0"/> (test is also missing the catalogue number and format)