[MQTT-4.3.2-2] QoS = 1 delivery protocol (receiver)

[francois-normandin]

In the QoS 1 delivery protocol, the Receiver

MUST respond with a PUBACK Packet containing the Packet Identifier from the incoming PUBLISH Packet, having accepted ownership of the Application Message.
After it has sent a PUBACK Packet the Receiver MUST treat any incoming PUBLISH packet that contains the same Packet Identifier as being a new publication, irrespective of the setting of its DUP flag.