What I expected was: I would be blocked by blocks that I walk into at head height

What happened was: Walking/swim-walking into blocks that are at head height and has a non-full block (ex: fence gates, cobblestone walls, water) beneath. Take suffocation damage, and easily walking back out of the block. You get blocked by smaller hit box of the block beneath but head is partially in the larger hit box of the block above.

Steps to replicate: 

1. Swim in water with elytra equipped.
2. Then walk into block at head height with non-full block such as water, cobblestone walls, or fence gates.

Jumping multiple times makes problem stop for the moment. To reactivate glitch, repeat steps again.

 Attached below are 2 different examples.