AMD RX 460 GPU multiple layers incorrect render I've come across this weird issue.

I have two layers I want to render and combine. Those were set up with the "Setup Tracking Scene" button. The first layer always renders without problems. However, the layer that contains my shadow catcher renders with the top of each render tile's top missing, or artiffacted (based on what tile size I choose). But when I turn off rendering for the first layer, the second one renders fine. Also, if I render on my CPU, everything renders OK, but it takes about twice as much time (I'm using an old Athlon II).

Here's what the scene looks like:

And here's the background layer rendered:

I'm using cycles in Blender 2.78, on Arch linux. My GPU is an AMD RX 460.
AMD has a long history of issues with blender.

Try updating the drivers for your card. 

There has been a lot of work lately to get AMD to play nice with blender, try using one of the latest builds: https://builder.blender.org/download/

Otherwise it looks like a bug. Please read the following link: Best place to put bug reports?