I'd also very much like this answer as well.
Not only is the total vote count skewed, but the "voted" cookie is also set, so
if somebody mistakenly hits the vote button without making a selection and then tries to correct their mistake, they are told they already voted.
For what it's worth, I think a page recycle would be the best solution rather than an error message of some kind. (but let's see if we even get that far first).