Is this the same thing thisnameistaken reported? Going to a window and back to full screen causing a strange video bug?
If so then I guess you can solve it by turning off "Window while connecting".
I have no idea how changing to window and back could cause a problem. I don't remember changing anything in that part of the program, though I will keep investigating.
EDIT : OK - I've reproduced that bug here. I'll fix it tonight or tomorrow. As thisnameistaken said - it's only a problem if you start LFS in full screen, then switch to window and back to full screen.