What likely happened is that you had a brief disconnect and the server may not have received your move.
The server is the keeper of the accurate time. With the lag compensation algorithms the times on the clients may not be accurate. That is why you may occasionally see clocks adjusted in games, even without increments.
ok I'm not that great but. the Damn thing forces me to resign. every time it happens to someone, they get there time back and I never do, or the countdown to force resign starts in the last minute, when I've been waiting 6- 7 minutes for there move like why. it's so frustrating does this happen to anyone else