The bug

If the player is gliding with an elytra and uses a spyglass while in third person view, the spyglass points down instead of the direction in which the player would see through it in first person view.

How to reproduce

1. Fly up, then face towards the horizon and glide with your elytra
2. Switch to third person view
3. Extend a spyglass
4. Notice how the spyglass is not pointing in the direction you are looking, but rather it is pointing down