Had something similar happen at dm - a drugstore here in Germany. The cashier asked if I had a payback card and inspite of me showing and her scanning it she scanned another barcode. On questioning her it turns out she registered me for the 5x promo that was running at the time (for which I had registered). Her supervisor had told her to register everyone to avoid discussions later when people whine that their 5x promo points didn't post.

That aside, the loyalty programs do some data mining to check if there are employees scanning their own cards over and over at the same vending point more than a feasible amount of times a day @:-)