I am a software developer/troubleshooter. Here are my thoughts on possible reasons: Both mine and my opponents connections were good (full green). As I said, it only happened yesterday in 2 games, but they were the first games of the new browser sessions. I was using ie8 with all updates. To get to the sessions, I type http://chess.com/simple. Did new game and it automatically brought one up. I think there must be a delay situation where the controlling entity thinks my board is active, but it has not been activated yet. I will be playing more games today and post if it happens again.
I have in the past regularly seen where my opponents time will go up, but that is when there is a slow connection and I assume that it is because the timer for my opponent on my board is local and if there is a delay posting my move to my opponent, the time is not charged to him, but just ignored which makes sense. In thinking about it, this is what seems to be happening without ignoring the time. It is instead being charged to me when my opponent moves and not after I have seen him move. Somehow, the server must think that I have received his move when in fact I had not and then when the server syncs the times again, it revomes some of mine.
I have played several games today, but in 2 of them, I keep losing time when it is not my turn. I am playing 5 minutes with no extra time. I will move immediately, but when it becomes my turn, it will remove some time, usually about 5-10 seconds. It has only happened today.