In this post, Robert William Hanks has three of the same comment, and all three claim to be upvoted by me. But at the time the comment was originally posted, there was only one comment there, and that was the only thing I upvoted.
Just thought you'd like to know.
Here is a screen-shot (9/3/10):
It happens from multiple computers and multiple browsers, but only when I am logged in; I see only one comment when I'm logged-out.