Weird artifacts with post processing material

Hey! So I tried making a Lens Distortion material (pincushion distortion) and using it as post processing, I succeeded but I have a bunch of artifacts on the screen.
I followed this UE4 tutorial: Unreal Engine 4 - Lens Distortion Tutorial - YouTube

This is how it looks like in UDK:

Any clues on how to solve it?

I think that you may need to dive into source code if you can : P … maybe I am just saying that the problem is the engine not that you may have made a mistake. I am just saying ideas…