Rebuilding categorys seems to only rebuild the album_count, and it seems to get the data from media_count in xf_mg_category. I can increase/decrease the media_counter by adding/removing new media, but how do I get a recount of everything that is already in it?
Edit: Guess I found it. Categorys are not only defined in the albums, but also in the pictures themself (xf_mg_media_item category_id).