Above y=255, the debug screen crashes Minecraft when opened.

What I expected to happen was...:
The debug screen opens as per normal above y=255

What actually happened was...:
Instead, it crashed Minecraft

Steps to Reproduce:
1. Fly in Creative mode
2. Open debug screen (regardless of whether at y=255 or below) and continue flying upwards
3. Above y=255 the game crashes

Bug cannot be reproduced in 15w36d