1. Go edit any release and edit it to launch the release editor.
2. Go to recordings tab
3. Re-assign a track recording to a recording with comment, example : http://musicbrainz.org/recording/ef0cb6db-dd85-411d-9fe3-273f9c4a0e2d
4. See the comment appears
5. Re-assign again this track to a recording without disambiguation comment
6. See the track change except the comment from the previous recording is not removed, it is let in place.