processMessage is never called, processPacket works fine though

I converted this Ruby example to Scala, but the processMessage of the MessageListener a pass when creating a chat is never called. However when I add PacketListener, the processPacket method is called with packages which are instances Message - so the underlying part works well.

Also at the bottom of the Ruby example there is a note that the processMessage method is never called when named process_message but compiles without errors (interface contract is fulfilled). I guess both have the same source. Any idea if this could be linked to an implementation detail?