Crystallinesheen and Danlisa are right.
The problem really exist. I also saw it sometimes when playing. It's wheater transition related for sure. And it is like Danlisa described it: some annoying triangles on the sky dome.
I don't know if this is a stock bug or not. Perhaps it was really introduced by the adjusted scenes.dat?
I will carry this to GWX team anyway.
Thanks and welcome aboard Crystallinesheen!