from http://bugs.musicbrainz.org/ticket/4796

http://musicbrainz.org/show/edit/?editid=10178381 failed after my single No vote because the release was Low Quality. IMO, the only edits that should fail faster are those against High Quality releases.

I think a better solution would be to accept low quality edits faster (1 vote) and accept high quality edits slower (5 votes), leaving the fail count for all data qualities at 3 No votes.

from http://bugs.musicbrainz.org/ticket/2884

If you have a release at normal quality, and you edit to raise quality level to high, a single no vote is sufficient to end the vote.