JBoss Portal 4.3 logs "An error occured when trying to invalidate the sessions" messages

Issue

• JBoss Portal logs the following errors in the server.log file :

  [org.jboss.portal.server.listener.SessionListener] An error occured when trying to invalidate the sessions: null
  javax.servlet.ServletException
    at org.jboss.portal.web.command.CommandServlet.include(CommandServlet.java:97)
    at org.jboss.portal.web.command.CommandDispatcher.include(CommandDispatcher.java:50)
    at org.jboss.portal.web.jboss.JBossWebContext.include(JBossWebContext.java:66)
    at org.jboss.portal.web.impl.DefaultServletContainer.include(DefaultServletContainer.java:190)
    at org.jboss.portal.server.listener.SessionListener.sessionDestroyed(SessionListener.java:111)
    at org.jboss.web.tomcat.service.session.ClusteredSession.expire(ClusteredSession.java:854)
    at org.jboss.web.tomcat.service.session.JBossCacheManager.clearSessions(JBossCacheManager.java:579)
    at org.jboss.web.tomcat.service.session.JBossCacheManager.stop(JBossCacheManager.java:535)
    at org.apache.catalina.core.StandardContext.stop(StandardContext.java:4477)
    at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1055)
    at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1055)
    at org.apache.catalina.core.StandardEngine.stop(StandardEngine.java:448)
    at org.apache.catalina.core.StandardService.stop(StandardService.java:576)
    at org.apache.catalina.core.StandardServer.stop(StandardServer.java:744)
    at org.apache.catalina.startup.Catalina.stop(Catalina.java:616)
  ....
   Caused by: java.lang.IllegalStateException: invalidate: Session already invalidated
    at org.jboss.web.tomcat.service.session.ClusteredSession.invalidate(ClusteredSession.java:710)
    at org.apache.catalina.session.StandardSessionFacade.invalidate(StandardSessionFacade.java:150)
    at org.jboss.portal.server.aspects.server.SignOutInterceptor$Invalidation.doCallback(SignOutInterceptor.java:192)
    at org.jboss.portal.web.command.CommandDispatcher$CallbackCommand.execute(CommandDispatcher.java:74)
  ....
  

• The above messages are logged during shutdown