Consider editing artist 'foo' to 'bar'. In the meantime, edit 'foo' to 'waffles'. The original edit should now fail (conflict), but it currently passes.
This is in for code review at http://codereview.musicbrainz.org/r/1436/ and is available for testing at http://test.musicbrainz.org
It would be even nicer if the system checked for conflicting edits before allowing the user to enter an edit, and if conflicting stuff is found, confront them with a nice warning message and possibly require to tick a checkbox, like with entering identically named artists.
This issue is now in beta testing on http://beta.musicbrainz.org/. It is pretty much only testable by edits that are auto edits though.