People aren't going to trust a receipt over the system they use. It's as simple as someone checking their computer seeing that OP never paid and then forwarding it to the right place. It's not like the cop has the power to override the system because that would be nightmare in terms of accountability and potential abuse.

Yea, it sucks and it's unfair, but there's nothing unbelievable about it. For any set of rules, there are always going to be people that fall through the cracks.