Tested with v8.08 - 09. The encoding is flawless, but in the end you get a non-playable MP4. However, the encoding from MP4 to MKV is fine.
This from NVEncC v8.09:

And if you go back to v.7.82:

The result is ok.
But I have identified another issue. In both versions - old and new - no psnr or vmaf is possible if you read from mp4. No error, but the status line is not being output.