Mirror Placing Problems

[Ashes-in-a-Can]

Sometimes, when I put mirrors on a lot, large white boxes appear, like they're coming out from the mirror. Can someone explain what's going on and, if possible, a way to fix it?

[mangaroo]

That sounds a lot like artefacts. Do the white boxes still appear if you turn reflections off in the game's options?

Also, could you post your systm specs, per the "Quick Summary" section in Game Help:System Specs?