The bug

If you're gliding in 1st person mode with elytra, and change to 3rd person, it will then update the elytra appearance to gliding. Then, if you land in 1st person and then switch to 3rd person, it will also then update the elytra appearance to still.

How to reproduce

1. Stand on a block
2. Go to 3rd person view, then back to 1st person
3. Start gliding
4. Go to 3rd person view
   (If you glide, do step 2, land, and then do step 4, it will present the same issue)

Whenever I do this, doing step 4 causes the wings to spread apart (or draw back together). This means that the elytra are only updating when you are looking at yourself, even though they should already be in the correct position when you switch to 3rd person view (the very tick you switch to switch to 3rd person it should be in the correct position ).

NOTE: This bug could be invalid due to how entity rendering and updates work (in 1st person the player is not being rendered yet)