Strange behavior (bug?) when updating xmp:rating outside of XnViewMP

[Bezier]

Hi there,

System is Win10 1809 64bit. "Settings / Metadata / Update when file is changed outside" is checked.

I use exiftool to change xmp:rating outside of XnViewMP. First time through works like a charm; XnViewMP automatically updates the rating correctly. However, changing the rating the second time on the same picture doesn't have any effect anymore. "Refresh" or "Update catalog from files" doesn't seem to do anything.

I go to the next picture, with the same result: First change of rating goes well; after that, no changes anymore.

Any idea?

Best regards,
Bezier

[xnview]

The date of modified file is changed? 'Update catalog from files' doesn't change it?