AMQP sequencing error under heavy load

I am having a problem during a low-scale load test. The broker seems send an invalid delivery-id to the consumer which seems to violate AMQP protocol. This behavior leads to the client code disconnecting from the broker.

Steps to reproduce: use the Messaging Performance Tool (from master branch) to send a large influx of messages to the broker. (Obs.: I will provide detailed steps as an update to the ticket).