DomainTestSupport.Configuration.getSlaveConfiguration(String hostConfigPath, String testName, String hostName, WildFlyManagedConfiguration baseConfig, boolean readOnlyHost, boolean debug) drops any configured jboss.home from the passed in baseConfig, which results in the default one being used. That's fine for the normal testsuite/domain in wildfly core and full wildfly, as all the domain processes in those test modules use the same installation, just with different writable dirs per HC. But in mixed domain it means the legacy slaves are using jboss-modules.jar from the current version, not their own.

This is a minor bug as it seems to not cause any harm, but it could blow up somehow if something changes, and regardless it's not right to run a legacy slave that's not really running legacy software.