
Problem #1
Option Export Catalog's Category to XMP Subject and IPTC Keyword including two sub options Create XMP data and Create IPTC data is completely ignored and category is always exported to both XMP Subject and IPTC Keyword regardless of its being checked or unchecked.
Problem #2
Option Read hierarchical keywords from images as categories does not work, keywords always load hierarchically.
Perhaps to be more clear this option should be called "Read hierarchical keywords from images as hierarchical categories"
Problem #3
Option Write categories into images as hierachical keywords also does nothing, always write hierarchical.
There's typo in word "hierarchical"
Problem #4
Options Export rating in XMP metadata and Export color label in XMP metadata have no effect rating and color are always exported.
Problem #5
Option Write comment in XMP (dc:description and exif:UserComment) have no effect.
Perhaps because comments are not implemented yet.

Comments from Ctrl+D dialog box don't save in database, there's only option to write them in the file, and they don't get written to .XMP sidecar from there either when used with RAW files.
Problem #6
Tagging (checkbox) status is not exported from XnViewMP catalog to files with Update files from catalog

P.S. All above was tested on .ARW file and can be seen inside .XMP sidecar.