I recommend to use the jboss-ejb-client.properties (and not the remoting-project URL remote://... which is deprecated)
Have a look to https://docs.jboss.org/author/display/AS71/EJB+invocations+from+a+remote+client+using+JNDI
Does this work?
The reason is that AS7 is a new implementation andtherefor the ejb-client works different, specially in case of multithreading. There is a JIRA with enhancements EJBCLIENT-34 for this, but it is not finished right now.
Also I'll reproduce your issue and see how to achieve this.