Running build 1.2.0dec21031208 on Windows:
Steps:
1. Insert first cd of a multi-cd album
2. Press CD Lookup button
3. Select matching release and press OK. (Release loads into rightmost pane.)
4. Eject first cd
5. Insert second cd
6. Press CD Lookup button
7. Select same matching release and press OK.
8. Add folder of mp3s for both discs of corresponding album. (Tracks are loaded into rightmost pane.)
BUG: Tracks from second cd of album are given the musicbrainz_discid of the first cd.
Expected behavior: Tracks from disc 1 would get the first discid, and tracks from disc 2 would get the second discid.

http://forums.musicbrainz.org/viewtopic.php?id=4663