When merging a release, the merge is only shown under the release artists. Since merging releases also merges the recordings, this means that people can merge recordings on Various Artist releases without anyone subscribed to the track artists knowing. Since recordings can be shared by tens of releases, this makes a single bad merge a complete nightmare to fix.
See http://forums.musicbrainz.org/viewtopic.php?id=3332 and the discussion on http://chatlogs.musicbrainz.org/musicbrainz/2012/2012-01/2012-01-03.html for a real example. That track alone was linked to about 70 releases before bitmap started fixing it and there are another 15 tracks on the release that need fixing.