There is also some sock-puppet detection as well - this is to prevent you creating accounts and upvoting yourself. Presume it also prevents you downmodding ever

There is also some sock-puppet detection as well - this is to prevent you creating accounts and upvoting yourself. Presume it also prevents you downmodding every comment by someone you don't like too... I've seen it occasionally go awry - you'll upvote and the vote just disappears.