All our eggs in one basket?

If the bank sent you a coin and you claim you never got it (maybe you're telling the truth, maybe not), they can just send it again.

In fact, if the bank signs a committment to give you a particular coin, the bank can't claim to have never received your request. For high value transactions where timeliness is a concern, this prevents the bank from claiming that they didn't get the original request and thus making a "delay of service" attack against you. Delay of service is the denial of the service of timeliness. Eric