Really strange, are you using my ini?
Could anyone else try to reproduce it with cache enabled please?
Hmm.. so it doesn't work at all now!?
Edit: OK, so after xnview restart there are 2 files (from 2 folders) in Tag "category"!! And it's working again - and now it works perfect.
Edit2: So I can reproduce it only in one folder, in other folders it works good, but when I enter 'that' folder, tagged files are lost, when I restart xnview, they are all back. Very strange, it's nothing special on that folder, no special character in the name of folder or name.
Few screenshots (last after using "clear all tags"):
