The Bug:

You cannot use an Elytra to crawl into 1 block tall spaces while standing in a 2 block tall space. The game will instead constantly teleport back, as if you are trying to crawl through a ghost block. This works in both multiplayer and singleplayer. If you sneak to lower your hitbox or are in taller spaces, it will work fine.

Steps to Reproduce:

1. Build a 2 block tall space.
2. Build a 1 block tall space adjacent to it.
3. Stand in the 2 block tall space and face the 1 block tall space.
4. Put yourself into survival mode and equip an Elytra.
5. Try walking into the 1 block tall space and pressing the jump button twice quickly.
   You cannot enter the 1 block tall space.

Observed Behavior:

The player cannot use an Elytra to crawl into 1 block tall spaces while standing in a 2 block tall space.

Expected Behavior:

The player can use an Elytra to crawl into 1 block tall spaces while standing in a 2 block tall space.