I understand now. This was done on purpose. Since the software reads actual CD tracks, it supposedly knows precise duration of each track.
Still, if you would like to correct it (e.g. to match durations printed on cover), you can do so by duplicating album:
1. Select the album
2. Menu Tools - Duplicate
3. Delete the original album, but keep the copy
4. Edit the copy. All fields should be editable now.
Andrei