Reading ratings from XMP and JPG

Hy,

at the moment I Keyword an Tag my Photos with PhotoMechanic. Photo Mechanic stores these informations for RAWs in an XMP-File and for JPGs directly in the JPG.
When I change the rating of a Photo, after it is imported to C1. C1 doesn't read these information completely.

The options are set to load. With the checkboxes below I cannot get a complete solution.

Here are the effects of the checkboxes:

both activated: C1 reads only the XMPs
no one activated: C1 reads only the JPGs
first activated: C1 reads only the JPGs
second activated: C1 reads only the XMPs

So when changing the rating of Images in PM, I don't want to reimport the photos in C1.

For a test I tried to change the option to "Full synchronization" and do the rating in C1. Then the problem was, that C1 did not remember his own ratings. After restarting C1 the ratings have been gone.

Is this a problem with no possible solution at the moment or is it a mistake by me?

Thanks for your answers
Robert