Sky color depends on absolute height in world and changes abruptly

The bug

When the camera is below minimum world height (feet at about y = -65 by default), the bottom half of the sky suddenly goes dark.

How to reproduce

Generate a void superflat world, and fly down to the void. The lower portion of the skybox will abruptly flash to black.

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

This happens when the player eye level is below net.minecraft.world.World.getHorizon() which might be done to not have a blue blackground when you are in caves. It would be good if this effect was achieved differently.