FULL PRODUCT VERSION :
java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_04-b05)
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
For a non-Open MBean, an operation with a void return type results in an "Operation Completed Successfully" message. For an Open MBean, where the return type is specified as SimpleType.VOID, invocation results in a "Operation returned null" message.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create an Open MBean with a void operation. Register with a the MBeanServer. Start jconsole, navigate to the MBean operation, invoke it.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
"Operation completed successfully" message (as per non-Open MBeans)
ACTUAL -
"Operation returned null" message (as per non-void operations that return null)

REPRODUCIBILITY :
This bug can be reproduced always.