I have been awarded the silver haskell badge not too long ago. However when I checked my profile today to see which bronze tag badges I was awarded, the silver haskell badge was no longer there.
First I thought that maybe a haskell question I answered has been deleted, putting me under 400, and the addition of the bronze badges caused a batch recalc (though I can't imagine why it would). However when looking at the stats page for haskell, I still have more than 400 upvotes, so that's not it.
Edit: Thinking that maybe the stats on the stats page were cached and didn't into account deleted answer, I went through all my haskell answer and I definitely have 420 upvotes from non-deletet, non-community wiki answers (the stats page says 419, but I assume that's because the 420's upvote was from three hours ago and the stats page doesn't update that often). So still no idea, why I lost the badge.