Apologies for posting yesterday in the contest entry thread.
In response to XL2's Unreal demo:
"Impressive demo! I didn't get too far. After finally finding the tunnel above the beginning area, I dropped down to the lower area on the other end of the green tunnel and got clipped through a wall and slowly pushed diagonally upward.
Level geometry inside the walls continued to render normally but everything out of bounds would never clear previously rendered frames, meaning that as I panned the camera around, the level interior would leave a trail of static frames behind through the space out of bounds, much like those old screen-savers with the geometry that left trails of itself behind as it bounced around the screen."