So the problem is indeed TCCL usage from the Stub fork, along with a reference to a com.sun class:
http://anonsvn.jboss.org/repos/jbossas/projects/specs/trunk/jboss-rmi-api_1.0_spec/src/main/java/javax/rmi/CORBA/Stub.java
The reason it works occasionally is that when TCCL is null Class.forName falls back to the JDK which can load the sun class. When it is not null it tries to load it from the leaked TCCL which according to your log is the server module which doesnt cotain the class.
So it seems like we just need to port that stub base clase.