Even more funny is that in USA, the actual amount charged to the card is mutable. Take for example when you go to a restaurant and give your card, it's charged, and then you write out with a pen a tip amount, which at some future point gets added on to your charge.
But there are laws about that: you authorize tip with your signature, if they charge you more than you authorized, they can get in trouble. Don't see the issue here.
