REGRESSION: Mustang b53 breaks the cascading feature of JDMK

Starting b53, an MBean unregistered from the cascaded MBean server remains live on cascading side.
The JDMK used is 5.1 FCS, all platforms.

Attached a Java code that does:
- create cascaded MBS + register an MBean in it
- create a cascading MBS
- create a cascading service + mount the cascaded MBS
- prints true/false whether the the MBean is seen both a cascaded and cascading level
- unregister the MBean from the cascaded MBS
- sleep 7 seconds
- prints true/false whether the the MBean is seen both a cascaded and cascading level

That latest step shows that with b52 the MBean is not registered at the two levels as with b53 it remains registered at the cascading level only.

Also attached are the output of that test code run with both b52 and b53 in debug mode for both rmi and jmxmp protocols.