This question already has an answer here:
Got a weird (or neat) bug here. This question was migrated from music.SE to sound design beta. I happen to remember that I upvoted if not all, all but one of the other answers on the question. However, since it has been migrated to sound.SE, although the answers preserved their votes from music.SE, I am able to upvote them again.
I remember, for instance, that I was the only one to have upvote the accepted answer. My upvote is still there, but I can upvote it again, giving me a double-vote power.
Not a critical bug, but still a bug that could use working out.