The Bug:
Players' elytra don't move with the yaw of their bodies when swinging.
Players' worn equipment usually follow their motion in every other instance but this one.
Steps to Reproduce:
Equip elytra, look directly down, and switch perspectives once (hit F5 once).
Punch the ground constantly and observe the movement of your body and your elytra.
Observed Behavior:
Your elytra remain completely still despite your body rotating.
Expected Behavior:
Your elytra would rotate with your body.
I’m able to reproduce the behavior in question. It has been present in the game since the addition of elytra in Minecraft 15w41a.