I just downvoted a comment as "disagree with viewpoint".
The comment had 1 vote and no rating. As soon as I voted, the comment went rating 100%, with two votes, as if the two votes were upvotes. But if downvoting for disagreement doesn't count for rating, I'd expect the rating to remain unspecified, because still only 1 vote which counts for rating is there. If rating was unspecified before my vote, it's reasonable to expect it to remain unspecified.