LG M228WA-BZ Help !

Hi i finally bought one of these monitor/tv screens and i have been really happy with it, i mainly use it as a monitor and its used as a TV (Freeview Recorder) occasionally, but i have a question, i was running a PC game at 1280 - 720 in full screen and then i wanted to put the screen in windowed mode so it could run while i continued doing something else on the rest of the screen, but i noticed that the game seemed to judder, but not in a hardware lacking sense, but almost a sync sense. I've checked sync is on in the game and it is and works fine in full screen, any ideas ?