Looking good, man!
I think I know what you're saying. It won't return anything if you select, say, both 14th Street and H street because there are no posts tagged with both of those. It will only return results if you select only one of those. However, if you select both Downtown and American, you'll find something because there are posts tagged with both of these.
I think what you want is the option to broaden the results rather than narrow them, so that if you select both 14th and H Street, you'll find posts at either location, rather than posts that are only at both locations. This is a much requested feature, and I plan to look into it tonight, though if I can't finish it tonight, it may have to wait a week or so 'cause I've got a different task to do this weekend.