The mapping-module option "module" in a security-domain is dissapearing

Issue

We created a custom mapping-module, installed it as a JBoss module, and configured it in a security domain.

<security-domain name="accept-all" cache-type="default">
   <authentication>
    ...
   </authentication>
   <mapping>
    <mapping-module code="our.security.mappingmoduleCode" type="role" module="our.mappingmodule">
      <module-option name="roles" value="ALLOW-ALL"/>
    </mapping-module>
</mapping>
</security-domain>

When JBoss starts, the module gets loaded just fine.
As soon as we make a configuration change that makes JBoss rewrite the configuration to standalone.xml (domain.xml) the "module" option is gone and a subsequent start of JBoss fails.