I have unchecked "Use full screen" in the video options and restarted the game but it's still full screen. The box remains unchecked but I can restart again and it's still full screen.
Prior to 3A, there wasn't any problem to have it windowed.
Here is the debugg if it helps:
(Fortunately, Jing now works with Elemental full screen while it had to be windowed before so it's not hampering the testing)