What's got me confused is what exactly is the effect of a downvote? I downvoted a post, and my downvote was the only vote (up or down) it had received. When the UI refreshed, I was still the only vote, but his payout had gone from 0 to ~50 cents. How can a downvote give the poster rewards? I checked it on steemd.com too to make sure I was the only vote, and I was.

I haven't bothered to read the code yet to figure out what exactly a downvote does.