Every time I have my Terrain Manipulator out and I drag my cursor over the infinite source (any type), the terrain loses its reflections. At daytime, the ground becomes darker, but when it's nighttime, the ground just loses its reflections. Sometimes when I hover over the infinite source, the entire screen has a weird overlay like if you put the game screen on top of the game screen and make it transparent. I was playing the Steam release of the game.
Before:
After: