When I fly above y level 255 my character vanishes in F5 mode

What I expected to happen was...:
My character to not vanish

What actually happened was...:
My character vanished

Steps to Reproduce:
1. I flew upwards in back-facing F5 mode with the debug "screen" open.
2. When I passed y-level 255 my character vanished.
3. I was astonished so I went down below y-level 255 and the character appeared back again.
4. When I went back up past y-level 255 my character vanished again.
5. Not a huge gameplay-affecting issue I just thought someone should know.