Description
Delivery states with AMQP1.0 are open ended[1]. If the Broker was to receive a unrecognised custom delivery-state, it will currently fail. It should probably simply ignore delivery states that it does not recognise and continue processing the link regardless.
http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-messaging-v1.0-os.html#section-delivery-state