I downvoted an answer, and was surprised to see it show up in my own reputation history. I don't think I've ever noticed this happening on other Stack Exchange sites. The 1 point isn't important to me, but I thought it might be a bug. I didn't think up/downvotes affected the person doing the voting, or showed up in the voter's reputation history.
Or maybe my downvote was downvoted because I didn't add a comment with a reason. (Other people had already done so, and I didn't have anything else to add.)