A bug I've just noticed over the past two days... downvotes aren't costing me anything!
I downvoted something a day ago and noticed that my rep stayed constant (not supposed to happen), but the recipient lost 2 points (as should happen). I thought this might be a one-off bug or might be corrected at midnight, but that apparently isn't the case. I didn't lose a point overnight. Today, I saw another post I wanted to downvote, and noted my reputation (in case the same thing happened again). I downvoted, and again, no loss of 1 point. (The recipient, again, lost 2 points.)
EDIT: It should be noted that both of these downvotes were on questions, not answers. I just tried (and undid) an answer downvote, and the rep behaved as expected.
I've only downvoted 4 times in my whole SE career, so I may be missing something, but this doesn't seem right...