"Day" counter does not appear on debug screen when at y level 256

When you are at y level 256, the "Day" counter on your debug screen does not show.

How to replicate:
1. Create a new world.
2. Go to y level 256.
3. Press F3, or FN + F3.
4. The "Day" counter will not show, but if you go to y level 255 or below, it will.