It does show the vote, it just doesn't record a reputation loss because at the time it was cast, their reputation was 1 and could not go any lower.
Users receive a reputation recalculation shortly after their suspension which is what restores their reputation to its correct value. It also restores reputation loss for downvotes or any other inconsistencies that might have arisen due to the suspension.
Without calculating the true value of their reputation on every downvote, there isn't any way of knowing whether the new downvote would actually cause a reputation loss or not at the time it's cast. It's a lot easier and more performance friendly to just look at their current reputation and let it get fixed later.