I've been using xnView for years and it's just a great program! But now I do have a problem and I hope you can help me. I would like to save iptc-data to my pictures, but I don't get along with that dialog

I sorted my pictures to xnView-categories and my idea was to choose a category, mark all pictures, use strg + i and define the iptc-category. That woks fine as long as the pictures belong to just one category. But if, in a later category, there is a picture that has already an iptc-category, this gets copied to all other pictures.
Or, to say it in easier words: Take the first two pictures in a folder and give them the category A (iptc) and then mark the first and the third picture and give them the cat. B. The result is that the fist and the third pic have category A and B now. But I want the first one to have A and B and the third one to have only B. Is that possible?
I tried all combinations in the writing options but I don't get it. Is that really not possible or am I just to blind to see?
Thanks a lot for your help

best regrds
anke