Yeah, this bug didn't get it's wings pulled off till too late for release. Don't worry it's laying at the bottom of the kill jar and will be displayed for your enjoyment in our collection of dead bugs in a soon to come service release.

So you all know the exact trigger is actually was "No Lights with Map Shadows". If all the lights used reytrace or no shadows then this bug would happen. If you encounter the problem in a different situation (A scene using shadow maps) please report the problem. That's the only way it will get fixed.