JBoss hits IllegalStateException upon reload after adding modcluster subsystem

Issue

• We add the modcluster subsystem then reload through a sequence of CLI commands like the following:

[standalone@localhost:9999 /] /extension=org.jboss.as.modcluster:add
[standalone@localhost:9999 /] batch
[standalone@localhost:9999 / #] /subsystem=modcluster:add()
[standalone@localhost:9999 / #] /subsystem=modcluster/mod-cluster-config=configuration:add(connector=http,advertise="false",proxy-list="127.0.0.1:6666")
[standalone@localhost:9999 / #] run-batch
[standalone@localhost:9999 /] :reload

• This hits an exception upon reload:

java.lang.IllegalStateException: JBAS018786: Multiple Deployment Unit registered processors with priority class 7170 and class org.jboss.as.modcluster.ModClusterServiceWebDependencyProcessor
at org.jboss.as.server.DeployerChainAddHandler.addDeploymentProcessor(DeployerChainAddHandler.java:63)
    at org.jboss.as.server.AbstractDeploymentChainStep$1.addDeploymentProcessor(AbstractDeploymentChainStep.java:40)
    at org.jboss.as.modcluster.ModClusterSubsystemAdd$1.execute(ModClusterSubsystemAdd.java:96)
    at org.jboss.as.server.AbstractDeploymentChainStep.execute(AbstractDeploymentChainStep.java:50)
    at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:702) [jboss-as-controller-7.5.0.Final-redhat-21.jar:7.5.0.Final-redhat-21]
    at org.jboss.as.controller.AbstractOperationContext.doCompleteStep(AbstractOperationContext.java:537) [jboss-as-controller-7.5.0.Final-redhat-21.jar:7.5.0.Final-redhat-21]
    at org.jboss.as.controller.AbstractOperationContext.completeStepInternal(AbstractOperationContext.java:338)

• Deployment fails unpredictable with mod cluster active.