This seems not to affect only cards, but boxes of ammo, primers, and powder, too. Mind, with the Caravan cards is where I have the most trouble. When buying these pre-packaged items from vendors, they don't seem to reliably 'activate' post-purchase. With boxes of ammo and primer and so on I've dropped the item and picked it back up, which fixes the problem, but I am unable to add new Caravan cards to my deck, even by using this method.