So, another bizarre bug is going on. My concrete ceilings that I'm using nature/ground_04 are black except when I'm looking from one of a few very specific angles. Observe: The one on the left is OK because I changed it to concrete/concretefloor002b, but it was the same way before that. And I have other nature/ground_04 ceilings in the same map that are just fine! So I'm at a loss.