I was messing around in the options, seeing that a new fullscreen resolution slider had been added, then I realized the fullscreen button itself didn't work.

What I expected to happen was...:
1. Pressing the fullscreen button in the options/video settings menu would toggle fullscreen on and off.
2. After pressing the fullscreen button, it would say "on".

What actually happened was...:
The fullscreen menu defaulted to off and had glitchy effects, like the screen being fullscreen but the game being surrounded by a black border. The fullscreen button also does not toggle, and stays off.

Steps to Reproduce:
1. Go to the Video Settings tab of options
2. Press the fullscreen button

All posted screenshots were not using Minecraft's screenshot generator, as those don't demonstrate the glitch fully.