Resolution:
Here is an extract from the section Scalability of Incoming Events :

"You may use a protocol to distribute incoming events across multiple process engines, such as TIBCO Rendezvous Distributed Queues or Java Messaging Service (JMS) queues. This allows for greater scalability because the load of incoming events is distributed. However, if you have a "Wait for ..." activity, such as Wait for Queue Message, in your process definition, the incoming event is received by all process instances across the multiple process engines"

The above information regarding "Wait for..." activity is not relevant to "Wait for JMS Queue message", it is relevant to only "Wait for Rendezvous Message".