Put the summary of the bug you're having here

What I expected to happen was...:
The player would bounce off the slime block while flying at high speeds and take no damage, just like falling onto a slime block

What actually happened was...:
You hit it and take damage and your screen flips around.

Steps to Reproduce:
1. Get Elytra
2. Build a slime block wall
3. Obtain high speed
4. Fly into wall