Full Screen at the Start of the Game

Ok, so here's what happens.

After you get to the "MOJANG" screen, you get the title. Go on Multiplayer or Single Player, while full screen (F11) is on.
Go to your world or a server. You notice it shows the "Loading Screen."
It shows your world for a split second, then it lags, but usually, it CRASHES.

Sort of, I thought none of a sort that this would happen when I first signed up.

But really; my game has crashed mainly to this reason. Possibly other's computers.

On multiplayer, it plain right crashes the server as well. It say that the 'handler is invalid.'
This happens with other's computers. This is a very urgent bug.