My subdeployment is getting ClassCastExceptions in EAP 6

Issue

• I can't get JBoss to exclude a Java EE component from my deployment even though I've added an exclusion for it in jboss-deployment-structure.xml.
• When migrating an application to EAP6 I get ClassCastExceptions for classes provided by JBoss.
• I have an .ear with a .war subdeployment. I am including my own implementation of something that JBoss already provides (e.g. Hibernate, JAX-WS runtime, Log4J, JAX-RS runtime). I've correctly added exclusions for the component I'm using to jboss-deployment-structure.xml, but I'm still getting ClassCastExceptions. What am I doing wrong? Here is my jboss-deployment-structure.xml (this example shows Log4J):

<jboss-deployment-structure xmlns="urn:jboss:deployment-structure:1.0">
  <deployment>
    <exclusions>
      <module name="org.apache.log4j" />
      <module name="org.jboss.log4j.logmanager" />
    </exclusions>
    ...
  </deployment>
  <sub-deployment name="test.war">
    <exclusions>
      <module name="org.apache.log4j" />
      <module name="org.jboss.log4j.logmanager" />
      ...
    </exclusions>
  ...
  </sub-deployment>
</jboss-deployment-structure>