This is slightly OT, but I have to tell somebody.
I wanted to buy a 70p item from the office vending machine. I had the exact amount in my wallet. No problem with the first three 20p coins, but my 10p was repeatedly rejected. So I pushed the coin return button, and got nothing back. It seems the machine will give change, but it won't allow you to cancel a transaction if you haven't inserted enough money to buy something. I expect this would the source of a tidy profit, were it not for the cost of replacing wrecked machines. Who designs the firmware for these things?