When deployed to a cluster, the messaging engine created for the WebSphere Business Monitor service integration bus is only active on one cluster member at a time. This behavior is specified by the default service integration bus policy. While the default service integration bus policy can be customized, the policy must always be of type "One-of-N." A "One-of-N" policy allows only one instance of the messaging engine to become active in a cluster, providing high availability (protecting components and models from the failure of a single server), but not scalability (the ability to expand as resources are added).
I agree with above statement totally , but please understand what it is saying. It applies that in 1 JVM only 1 ME can be active at any point of time. You can never ever have 2 ME active simultaneously in 1 JVM.
And when in cluster ME automatically associate it self with first available JVM.
But when you define a core group policy then you tell your 2 ME to associate themselves with 2 JVM respectively as per your Core Group policy.
My question to you is - How are you so sure that your JVM are not sharing messages ?
and do check JVM logs for ME getting associated with the JVM. as the console will only give you statues whether they are up or not but Log will show which ME is associating with which JVM. And if you Core Group policy are correct ME1 will always associate with JVM1 irrespective of configuration and status of other ME2 and JVM2