Yes there was a problem introduced around 4.0.1.
A couple of work arounds are mentioned in the issue and related issues and the fix is included in JBoss 4.0.2 (Which looks like it has just two outstanding issues left before it can be released).
Workaround 2: Use a different MBean name for the service, e.g. if it is an EJB
use a different jndi name or in the RMIAdaptor case, just change the name in
the config file
I didn't understand this workaround. My problem is with RMIAdaptor. Can you give an example?