While you are in Minecraft Windowed mode, and then click the green "expand to fullscreen" button in the top left-hand corner, then go to Minecraft settings and toggle fullscreen on then off, it will push the Minecraft window halfway out of the screen and won't seem to be able to go back to windowed mode even if you click the green "expand to fullscreen" button again.

If you go to a new application while it is in the glitched fullscreen (game looks like it does in the picture), then go back to minecraft and try to toggle fullscreen back on, it will sometimes crash the client. Can't fully figure out what causes this bug.

Unconfirmed: One time, the mouse would freeze when going to the f3 or f4 screen to sort through applications in the bugged fullscreen. This didn't seem to happen more than once, but could be important.