Upvoting bug?

I just got an email notification that someone upvoted my post, but as I see it still has 0 votes.

So, it's either a bug or the person changed his mind and unvoted.

But I had this before, at least once, a few weeks ago with another topic (I don't remember which one). It's quite strange if people vote & unvote. 2 times already. So, I think it may be a bug...