The org.jboss.soa.esb.messagetrace property needs to be defined in the filters properties section:
<properties name="filters">
<property name="org.jboss.soa.esb.filter.1" value="org.jboss.internal.soa.esb.message.filter.MetaDataFilter"/>
<property name="org.jboss.soa.esb.filter.2" value="org.jboss.internal.soa.esb.message.filter.GatewayFilter"/>
<!-- add the logging MedatData Filter for message tracing -->
<property name="org.jboss.soa.esb.filter.3" value="org.jboss.internal.soa.esb.message.filter.TraceFilter"/>
<!-- enable global message tracing -->
<property name="org.jboss.soa.esb.messagetrace" value="ON"/>
</properties>