If you consider this edit:
http://musicbrainz.org/edit/14507839
A CD discid has been attached to 2nd medium (a 1-track DVD) of a release due to bug
MBS-1814.
Then FixTrackLength script used TOC to update track length of DVD, although:
- a DVD can't have a discid
- the number of tracks doesn't match between the TOC and the medium
This is now in for code review at http://codereview.musicbrainz.org/r/1258/