This is one for the big boss man sorry, not something mods can help with.
I don't know any details of this particular instance
... but i do know that Andy can see every single upvote/downvote that anyne has made, when it was made and who it was made for/against.
He told me some time ago that if you continually voted for/against the same person then your vote would lose effectiveness ... ie if i voted Rasputin, as a random example, down every post then my downvote would automatically begin to count as half a downvote and if it continued a third of a downvote etc.
Since then he may have decided that if there was a continual pattern in someone's voting habits of upvoting or downvoting hte same person rather than it being even-handed that the voting facility was withdrawn fro that person.
As previously stated .. he's the only person who can answer questions about the voting algorithm and facility. Afterall, he owns and codes the whole site
PS ... votes on the Politics Forum don't count towards anyone's totals