The sample jpegs, just have the two characters, hh in the keywords field and only in the IPTC section. The XMP section is the one written by the camera with a rating = 0 and does not have any keywords. Photo Mechanic's default IPTC/XMP preference settings are set to read XMP before IPTC. If you change it to read IPTC before XMP, in the upper left section : for Jpegs, Tiffs, PSD and DNG files, then you will see the keywords in Photo Mechanic's IPTC Info dialog and anywhere you use the Keywords variable. Make sure the box is checked at the upper right section to add embedded IPTC.
Now it will be a good idea to update the XMP section with the same keywords. Select all and then use the Update IPTC / XMP option from the Tools menu. This will copy the IPTC info into the XMP section so both sections are now sync'd. You should be able to add a color label, star rating or other info and still have the keywords available in the File Explorer Window. Do you have your File Explorer Window set to show Photo Mechanic's keywords and ratings? If not, then see my attached screen shot for this configuration.
--Bob