Kirk is right, of course, you should definitely first read the XMP-sidecar file (should have made that explicit in my earlier answer). If you (also) use Adobe products to edit metadata, Kirk's advice about not embedding the XMP data into your raw files is a good one.
Note: I personally only use Adobe products to edit my images, and perform all my metadata edits with PM (I furthermore generally do not use Adobe for my raw edits) so I do embed the XMP. This works fine too, but in this case you need to be aware of the possible snags, hence Kirk's advice to not use embedded XMP if you (only) use Adobe products.
Anyway, updating your preferences according to the advice should fix your problem.