Light levels in the F3 debug menu aren't accurate when standing on mud

The Bug:

Light levels in the F3 debug menu aren't accurate when standing on mud.

Steps to Reproduce:

1. Enable the F3 debug menu and place down some mud.
2. Stand on top of the mud and pay close attention to what the game states your light levels are.
3. Take note as to whether or not light levels in the F3 debug menu aren't accurate when standing on mud.

Observed Behavior:

Light levels always appear as "0" when standing on mud.

Expected Behavior:

Light levels would be accurate when standing on mud.