I have a shipped build for Windows and in the GameUserSettings.ini I have fullscreen as windowed initially. If you enter fullscreen mode with the F11 key and close the game, the GameUserSettings.ini file has FullscreenMode=1.
However, if you go back to windowed, and maximize it, the FullscreenMode field is removed in the config, and the next time you start the game the window position is not remembered (WindowPosX=-1
WindowPosY=-1 always)
and the top is cut off.
The top is the white bar, and thats the very top of my screen. The window is partially out of frame and not maximized.