This answer

structured vs. unstructured data in db

has a score of 0, but when I click on the score I see zero upvotes and one downvote, which add up to -1.

Refreshing the page does not help, nor does clearing the cache.

This looks similar to an older (fixed) bug: Voting on a question after having clicked the upvotes/downvotes count will display an incorrect value, but is not quite the same - I have not voted on this answer (I could not possibly have, because I am its owner) and I don't think it can be a cache or AJAX issue either; The downvote appears to be legitimate (it reduced my reputation.)