Kirk,
The xmp file was created spontaneously after importing GPS coordinates (screen copy:first date is creation date, second date is modification date, i forgot to capture columns headings).
The rw2 files are straight from the camera (via PM Ingest, just copy without IPTC stationary panel applied), then i have tagged the picture with PM, so the modification date of the rw2 file was changed, which proves that XMP info are -partially- embedded in the raw file. But I have the same behaviour with RW2 files really straight from the camera.
I hope this will help you
I can send you any extra information you need (I am currently supporting/debugging a large software application, so I understand your problems)
Regards
Frederic