I was gliding with the Elytra, and I opened my inventory. I should have seen a normal player model, gliding. however, the player model used in the inventory was inverted (I.E. it was flying on its back, with the elytra up.)

Steps to reproduce:
1. Equip Elytra.
2. Jump of a sufficent ledge and start gliding.
3. Open your inventory, your inventory player model should be inverted.

EDIT: Attempted this several more times. sometimes it worked as normal, and other times the bug occurred. I couldn't find a specific pattern to the bug either, sometimes it happened, sometimes it didn't.