When standalone JMS client with EAP 5 client libraries lookups CF from EAP 6 server then it can't create connection on it. It fails with:

Exception in thread "main" java.lang.NoClassDefFoundError: org/hornetq/core/server/HornetQComponent
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
        at org.hornetq.core.remoting.impl.invm.InVMConnectorFactory.createConnector(InVMConnectorFactory.java:40)
        at org.hornetq.core.client.impl.ClientSessionFactoryImpl.getConnection(ClientSessionFactoryImpl.java:1127)
        at org.hornetq.core.client.impl.ClientSessionFactoryImpl.getConnectionWithRetry(ClientSessionFactoryImpl.java:1001)
        at org.hornetq.core.client.impl.ClientSessionFactoryImpl.connect(ClientSessionFactoryImpl.java:225)
        at org.hornetq.core.client.impl.ServerLocatorImpl.createSessionFactory(ServerLocatorImpl.java:767)
        at org.hornetq.jms.client.HornetQConnectionFactory.createConnectionInternal(HornetQConnectionFactory.java:601)
        at org.hornetq.jms.client.HornetQConnectionFactory.createConnection(HornetQConnectionFactory.java:119)
        at org.hornetq.jms.client.HornetQConnectionFactory.createConnection(HornetQConnectionFactory.java:114)
        at org.jboss.jms.client.TestConsumerSimple.main(TestConsumerSimple.java:51)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.lang.ClassNotFoundException: org.hornetq.core.server.HornetQComponent
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
        ... 26 more

This is not affecting use cases which are using MDB/EJBs with (local) JmsXA connection factory but there is another customer who needs standalone JMS clients with EAP 5 libraries to connect to EAP 6 server.

Note there is new module for EAP 6 which allows EAP 5 client to do JNDI lookup to EAP 6. More info: https://mojo.redhat.com/docs/DOC-929745