When the game is in fullscreen mode:
Alt-Tab out of the game.
Alt-Tab back into the game.
Take note of the blue window outline that briefly appears.
Go to the deployment screen.
Notice how the blue window, although invisible, is still active.
Clicking in a certain part of the top left of the screen opens the windows alt menu.
The top half of the uppermost buttons don’t work, because now an invisible blue bar is catching the clicks.
Double clicking on the invisible blue bar causes it to lose invisibility and flicker for a couple of frames - as the game window resizes, and then it is automatically re-maximised by the game code.