I spent some time trying to help the OP on this question this morning. He evidently didn't like my answer, and gave me a downvote. How do I know? Well, when I deleted my answer, his rep immediately went back up by 1.
Now, I don't much care about the particulars of this question/answer (or my rep), but it seems to me that this is a potentially significant hole in maintaining the anonymity of voting. Obviously, this hole has only been possible recently -- ever since rep changes have become reflected instantly.
Also, this question is very similar, but doesn't take into account the ramifications of the insta-changes to rep that led to this scenario.
Should this be considered a bug?