This test sends an event to a SocketNode running in a different process. The test expects that the hostID MDC value set in the receiver is integrated with the MDC values sent over the wire. This magic apparently happens in Sun JVM's (though not obvious where it happens) but not on Apache Harmony. The temporary fix is to explicitly set the hostID MDC value if a Harmony JVM is detected. Needs further investigation to determine if this is an Apache Harmony bug, unreasonable test expectation or an log4j bug.