I am experiencing the same problem. At some stores the 'retourpinnen' just doesn't work, at others it does. And something else... Sometimes when the 'retourpinnen' doesn't work and I get an error in the store, the amount of money seems to be added after all, but hours later... So then there is the situation that I got the money back 2 times, with the card (which gave an error) and cash....