Ok...
I uninstalled PM5, PM6, deleted the Camera Bits AppData folder, reinstalled PM6 2818. I didn't have to re-enter my key, so is there additional data elsewhere?
Then i opened the folder with the images, went into an image and it reads no metadata except for a byline tag set by the camera.
Opening the corresponding .xmp file shows that there is in fact metadata, as I applied previously with PM5.
If I then modify the file in PM6, such as changing the colour class, it then wipes the .xmp completely.
Same if I enter data into a blank metadata field where there should be data, it wipes the .xmp clean