While working on my translucent glass material, I suddenly noticed the same stripes and artifacts Kingsal has in his Volta 2 mission for all the water materials. They weren't there before, but it looks like I had in-game anti-aliasing set to x2. When I turned it off, the artifacts appeared. To test this, I launched Volta 2 with in-game AA x2, and the artifacts were gone. It seems like there's connection between in- game AA and refraction.
I have no idea about engine programming, but isn't it something about engine precision? Maybe similar stuff to BSP holes and lower dmapping precision than 2.05? It seems like something got broken in that department.