Ah wrong combo i meant the force current view option in the menu. If you check that players can't pan. Don't know if there's a key combo for but you could check. You could also try turning it on and off when it happens again.
Do you mean "Center players on current view", in the Tool menu? If so, I've tried toggling that option as well as "Center players on current view (Continuous)".
I had one user who had that issue, but only one user.
I know this because I run two copies in my home, one on my laptop as a DM, one hooked up to my TV for the players who come to the game in person. The "TV" runs as a player, and I was able to pan, but the person via skype (many many many miles away) wasnt.
We run maptools every session, and this is the first time this has ever happened.