There seems to be a problem with the implementation of the getDeliveringMessages() method on QueueImpl class. The key used to store the values in the returned Hashmap is always the same so what it returns is the value for the last loop iteration.
This was resolved on the 2.3.x via 31be03a723faa6079e02a0e3de97b76ec3259a57.
Justin Bertram <jbertram> updated the status of jira HORNETQ-1477 to Resolved
*** Bug 1221494 has been marked as a duplicate of this bug. ***
Verified with 6.4.2.CP.CR1
Retroactively bulk-closing issues from released EAP 6.4 cumulative patches.