This appears to happen when there's subsecond stuff added by the discid; the track parser apparently truncates down for display (it's displaying something that's on the release as :21 as :20 in the listing). However, I don't know if it also affects track times that would be displayed rounded-down.

To reproduce:

1. http://musicbrainz.org/release/5ac38f64-27ec-3fe0-9c46-727f3537e877/edit
2. Open the track parser
3. Change anything in the title of track 7 (Juggling～acoustic GTR "turbo"starter～) – I just changed the capitalization of the j
4. Parse Tracks
5. Progress to edit note tab (you may need to select recordings in some cases)

You'll see that track 7 (and some others) have their times changed to one second smaller.

This will not happen if you just manually change the time without using the track parser.