Hey Elliott,

thanks for your reply. Actually the whole thing does only work when I upload the images within the portfolio entry (-> “Beitragsbild festlegen”) . When uploading pictures the common way as a media, they won’t show up in my gallery, even when I set a portfolio category. That’s why I was wondering if this is a bug or a feature ;-)
I made a screenshot from the Image Settings, there on the right side you can see the “uploaded to portfolio” (in german -> hochgeladen: zu portfolio).