Ah, I see I read the thing too fast. :-)
This is a classic problem of remote EJB invocation.
You could bundle the interface in both ear', and somehow make the Service.ear call a call-by-value.
(dunno if we support such fine-grained configuration)
Or we could go down the big-ball-o-mud path, imho a cool JBoss feature. :-)
Now I think the question is: how can I define classloading isolation in application.ear on a per-library basis. So that I can isolate the Seam libraries and stuff, but not the EJB's. This would resolve this situation, am I right?
I should be doable, yes.
Let me think about this, and get back to you.