At least I'm reasonably sure it's because of MGE XE. It's the only mod I have installed that would mess with something like this. What I'm experiencing is diagonal strips of darker shaded areas on the texture of the free-standing Hlaalu wallpiece (in_hlaalu_wall in statics) in the top-left and bottom-right corners, as such: http://i.imgur.com/6ZV29Jp.png and http://i.imgur.com/9Y4ZY0o.png

At first I thought that it was an issue with the light sources, because it seemed to be happening with some walls and not others, but when I TCLed outside the interiors in the second pic, that's when I realized it was only happening to the free-standing wallpiece, and not any of the walls that were a part of a floor-wall-ceiling tile.

So why is this happening and is there something I can do to correct it? Some setting in MGE XE that I should mess around with? Or some kind of patch someone has done to correct it?