Found what I think may be a classloading issue while working on the S-RAMP project.

We include RESTEasy in our WARs because we want a single WAR that runs in multiple containers and because we need a newer version of RESTEasy. If you deploy two WARs that both package RESTEasy, then you will get a ClassCastException. See the linked RESTEasy Jira issue I entered for this problem (I'm not sure if it's a bug in resteasy or jboss).

Ultimately it seems that a class is loaded from the RESTEasy module included in JBoss AS, despite that module being excluded via the jboss-deployment-structure.xml file.

A sample maven project showing this problem is included on the linked RESTEasy issue.