So far, it seems to be:
The first query gives me no results, the second gives me two rows:
TagName UpVotes ========================== javascript 10 hidden-features 10
What's strange about this is that I have an answer in Hidden features of JavaScript, which is tagged as above. My answer has 10 up votes, so it's as if the second query is only finding those up votes.
These queries worked before, so I'm not sure what broke them. I've tested them with a few user IDs from the top user list with similar results. I've also tried several other queries that worked fine. The same queries appear to work for the other sites in the main trilogy.