You can half fly underwater with elytra

When you crouch and press the sprint key the game tries to make you swim an activate the elytra. This causes you to not be able to swim up very well but easily sink to the bottom. This also prevents you from swimming off of blocks.

 

Steps to reproduce:

1. Go underwater with an elytra
2. Crouch and walk forward
3. Hit the sprint key and keep holding W