Linear Compositing resulting in image distortion once merged

Finally taking the plunge in to a Linear live action/CGI workflow, so far everything works really well and as expected when following Stefan Ihringer's srgb_rec709_viewshaders.

However, when I merge two linear images together it results in a distorted image with green pixels and tearing. When looking at the two ends of the flow, before the merge, all look as expected.

Included is a screen capture. I've blurred out the subjects, so that blurring is not the result of the issue. I'm merging by placing the output of the foreground node to the output of the background node, no blending modes are being used.