XnView Software

Select a photo with existing face tags , open "Face tag" add-on , and use a right click to delete all the tags. Write.
-> the corresponding XMP tags are deleted OK,

The catalog filter has still an entry for this (or these) person (s)

Settings : (metadata) Import xmp keywords enabled. Import xmp face tag enabled.

Thanks to your detailed description I can reproduce the problem.

This problem is supposed to be fixed in XnView MP 1.7.0. Please check and confirm the bug fix here.

Fixed