Z-depth pass shows darkening around the edges like vignetting

[Alex_M]

It seems that there's a problem with the Z-depth pass. I tried with multiple scenes and with standard and vray camera and it's always the same - darkening around the edges as if there's vignetting effect going on. Rendering a Z-depth pass with Scanline gives a correct result. Please check the attached image. Max 2018.4 + Vray Next 4.02.04.00005.

[Alex_M]

Anyone? BTW, it seems that this problem occurs only when the camera points straight down.