What I expected to happen was...:
I was holding the sprint key so I could be sprinting when I hit the ground, and then noticed my FOV changing before I was no longer using my elytra. I thought it was fine until more testing I found that if you are holding it in the air it can sometimes change your FOV back and forward very quickly. I know I can just turn off FOV effects and it wont be a problem.

Steps to Reproduce:
1. fly up into the air with a rocket or fly from a height
2. hold Ctrl (the default sprint key) + space + W
3. try not to hit the ground and see if it happens