In beta2-SNAPSHOT the behaviour is a bit different. For the first chat message I receive three ACKs:
SENT (0): <message to='7154a5d8af3e4221976d374b2f05e4c1@localhost' id='rm2mi-13' type='chat'><body>hhhhhh</body><thread>7154a5d8af3e4221976d374b2f05e4c1@localho st</thread></message>
processPacket ACK: rm2mi-5
processPacket ACK: rm2mi-6
processPacket ACK: rm2mi-13
After that it behaves as I would expect.
When I register for the specific packet ID, the processPacket() callback is not even called.