The bug
Due to the fix for MC-3615, there is an angle which causes the fog overlay to apply then when it shouldn't.
This is also fully reproducible in survival mode.
It seems if you aim your camera at -23.8 and go into second person, the lava overlay applies. The problem is, it goes away as soon as you move your camera to -23.7 or -23.9. Moving your camera both up or down causes the overlay to disappear, which does not seem intended in the slightest.
How to reproduce
Create a Redstone Ready Superflat
Press
F5
once (or whichever key you've mapped to toggle perspective) to go into second person perspective.Run
/fill ~ ~-1 ~-2 ~ ~-1 ~-4 lava
Run
/tp @p ~ ~ ~ 0 -23.8
Results: The screen is red.
Expected results: The screen won't have the lava overlay.
Can confirm. Seems to happen exactly when the camera intersects a .0 Y plane.