In terms of the $proxy being returned, I see that is perfectly normal (I had a feeling it might have been).
The classcast exception only occured for JBoss3.0.0alpha, it is okay with beta, so I guess something got fixed in the transition. I do see there had been some problems with the ejb-ql parser, so maybe this played a role in it.
Now the decission whether to move to beta yet? I have noticed that it has the habit of bombing every now and then when an application is re-deployed. You then need to delete the tmp folder contents and restart.
All the best,