OK it looks like our logic for loading IPTC (IIM) vs XMP has a bug that apparently only affects Windows systems, and only when you have a RAW file that has embedded IPTC only. No embedded XMP or XMP sidecar. The sample file you provided has no XMP at all. This combination causes PM to ignore the embedded IPTC in your NEF.
We have a fix and this will be included in the next update to PM6. We will update you directly with a test build.
One temporary workaround would be to "touch" the files using PM5 (make some metadata change that would cause XMP to become embedded or put into a sidecar). I suggest you contact our support department on suggestions for this (one way is to select tagged, then un-tag and re-tag, then select inverse and tag and un-tag).
Thanks for reporting this.
Regards,
--dennis