I'm still playing with this issue myself, but I think the answer probably lies in this Wiki entry on JBoss classloading:
Glad I found that to better understand how classloading works in JBoss/EAR's/EJB's, as well as had dejanp reply and send me down that path.. hopefully I'm finally about to get this thing working...
Changing the ear-deployer.xml file worked for me! I'm going to try and create EJB configs to accomplish the same thing however so I don't have to have this file changed in all of the various dev/qa/prod JBoss env's however.
Let us know if you have found a solution to the prob by changing jboss xml file.