When I worked in Sainsbury's those two deals on one product cock ups were quite common. Once with nappies was the best one; the deals together actually took it into negative money, and while you couldn't do it and get cash out of the till, you could then use that to subsidise other products. My mum found it a bit strange me turning up at home with 24 cans, 40 fags and 6 boxes of nappies, mind.