Windowed>Fullscreen

Razukee

I'm not sure how persistent this effect is (If a restart fixes it for instance) but if you're in windowed mode and you make the window smaller and you then try to turn your game into fullscreen or fullscreen window, the game will remain in it's "Small format"

There's also the possibility that upon returning to windowed fullscreen that the gamescreen will be off-center towards the bottom (You can see the desktop above it and can't scroll to the bottom of the screen to pan in-game)