The following code from DefaultMBeanServerInterceptor::internal_addObject() should
be modified to take the postRegisterInvoke() out fo the synchronized block:

        synchronized(this) {
            try {
                repository.addMBean(object, logicalName);
            }
            catch (InstanceAlreadyExistsException e) {
                if (object instanceof MBeanRegistration) {
                    postRegisterInvoke((MBeanRegistration) object, false, true);
                }
                throw e;
            }
        }