the bug when i change the size of game screen

when i change the size of my minecraft screen,i find one thing!!that is look like a cheat
when my mouse was put on minecraft screen border,all the game will stop running,that was not only happen in Single player,also in Multiplayer server,although a lot of server have a no cheat plugins,but some of server have not,it will make player won't drop as fast as original,and it will make those player can't got the damage from monster or player,it is bad for some minigame server,please fix it,i don't want to have so many cheating player