So, I was flying around the world I made about an hour ago, then I set off on my elytra, which I was having bad luck with. I then got it working again, and started to fly around with the fireworks. I then found a desert and accidentally hit the ground, and my elytra was still going and I wasn't doing the leg-wobble thing. I then looked upwards and got launched off again. (In the image, the shadow is me.) (You can move around while in the ground, you move really fast. But no suffocation happens)

Steps to replicate
1)Get an elytra and fireworks and fly around.
2)Smash into the ground, and you might get stuck into the ground.
3) Look up. You're free!

EDIT:
Tried again and got stuck, really slowly. Fireworks aren't speeding me up.