Premoves DO take some time (around a tenth of second) to be effective, so in this particular case it might be the problem. I learnt it when premoving a 8-move checkmate sequence in dire time trouble.
As for the rest, there are thousands of forum topics about disconnection, the answer might be in one of these. You might want to check these. As far as I know, disconnection might make the opponent's timer go up from your point of view, but your opponent shouldn't have more time than you do.
Seems like some players have the abillity to temporary disconect in a way that only their opponents time get drained! happens quite oftent in bullet play! Happens when the opponent is losing! Last time it happended I had a premove in, which was a check, but even then it was only my time which ran out. Anybody else experiensing this?