See repo case attached. (I'm not sure it worked in 1.3, first time I have to use it)
The included EXR is the rendered output from the included max scene.
The screen shot is from After Effects showing only the red channel (x coord) of the pass. I have to dial in pretty big numbers for black/white-point before anything shows up, the 'hard' black/white boundaries are some sort of clipping.. the don't move when changing values. And the gradient looks like there is some sort of curve applied..
A CTextmap with a 'world coords' datamap gives the same result.
Nuke shows the same problem so it's not an AE issue.
using up to date max 2016