Game defaults to full screen upon launch even if you turned full screen off

When Minecraft launched it was in full screen, even though I had full screen off. I turned off Full Screen, closed out Minecraft, and then relaunched Minecraft. Full Screen was on again even though I had turned it off.

Edit: Just booted up the game again and it didn't boot into full screen. I don't know why it did it before, however, I think it may be something that happens randomly.