I've not had chance to reproduce this, but this is what I think I did:
1. Start Wildfly with the standalone-xts.xml configuration
2. Deploy a plain (non-XTS) web service to the server
3. Invoke the web service from inside this server, ensuring that org.jboss.xts is not in the dependencies. Which it shouldn't be if you are just invoking a plain WS.
4. Observe the CNFE on one of the TXBridge interceptors (I don't remember which).
I think the problem is that XTS is adding the handler chain for doing default context propagation to all web services, rather than just those that have the XTS dependency.