I can't comment because lack of reputation but it showed the achievement. I've tried to comment but of course I failed.
Take this example: Bob has 60 rep Bill accepts Bobs answer, Bob has 75 rep We trigger a message telling you now you have the bounty priv. Bill unaccepts your answer Message is stuck in the inbox. Obviously, the right thing to do is to pull the message out of the inbox, but that will require a fair bit of redesign to keep the process efficient.