Update: I've tried on 3 different machines across 5 different browsers now, and this problem persists across all machine / browser combinations. I created an ac

Update: I've tried on 3 different machines across 5 different browsers now, and this problem persists across all machine / browser combinations. I created an account and tried with that, and there was no problem upvoting anything. So, it would appear it's a problem with my specific account somehow. Thanks to everyone for helping figure out where the problem might at least lay.