When doing request/reply over JMS then by default a single threaded listener is used to orchestrate the reply as they come back.
If you want to process the reply message concurrently, you would have to use threads EIP as well.
However we should allow end users to configure the concurrentConsumer/maxConcurrentConsumers options.
This can be supposed for Exclusive reply queues, but would be more troublesome for shared reply queues. We had issues with this in the past.