I made the same experience as you. The proposed configuration in jboss.xml doesn't work. I am using JBoss 3.21.
If I change the MaximumSize of StdJMSPool in standardjboss.xml I can limit the mdb instances to one:
This seems to work, but I'd like more to do this in jboss.xml for a specific MDB.
You can configure <invoker-proxy-bindings>
in jboss.xml and reference them from your beans.