See http://musicbrainz.org/release/8fd13191-2d9a-4670-b789-0c99a06278e0 and then http://musicbrainz.org/ws/2/release/8fd13191-2d9a-4670-b789-0c99a06278e0?inc=artists+artist-credits+recordings+media

The track AC for "A track." is "MusicBrainz Test Artist #1 & MusicBrainz Test Artist #2." The above web service query only returns the AC for the recording, which is "MusicBrainz Test Artist 1 & MusicBrainz Test Artist 2."

There should be artist-credit nodes under track nodes if ?inc=artist-credits is specified. (Perhaps only if it's different from the recording's?)