The Bug:

I was playing around with ender-pearls in a creative test world then I accidentally teleported inside of a glass block. For a split second, I saw a glimpse of a black screen so I decided to experiment. I got some pistons, redstone, and some glass and I trapped myself inside of a glass block and instead of seeing through the block while in it, I was only shown a black-ish screen which is not something I expected.

To reproduce:

1. Create a piston mechanism that will enable you to get squished by glass blocks and prevent you from crawling.
2. Somehow activate the said pistons.
3. Observe the black screen.
   → You wouldn't expect something like this to happen to a transparent block but apparently it does which leads me to conclude that this is a bug.

Screenshots: