The following exception is thrown when the user changes skins for the second time immediately after changing the skin for the first time:
Caused by: javax.faces.FacesException: Cannot remove the same component twice: pbG9dea276d_2dee9e_2d4150_2dad91_2d22255b5a57d2_j_id1:j_idt444
at com.sun.faces.context.StateContext$AddRemoveListener.handleAddRemoveWithAutoPrune(StateContext.java:489) [jsf-impl-2.1.13-redhat-1.jar:2.1.13-redhat-1]
at com.sun.faces.context.StateContext$AddRemoveListener.handleRemove(StateContext.java:371) [jsf-impl-2.1.13-redhat-1.jar:2.1.13-redhat-1]
at com.sun.faces.context.StateContext$AddRemoveListener.processEvent(StateContext.java:334) [jsf-impl-2.1.13-redhat-1.jar:2.1.13-redhat-1]
at javax.faces.event.SystemEvent.processListener(SystemEvent.java:106) [jboss-jsf-api_2.1_spec-2.0.7.Final-redhat-1.jar:2.0.7.Final-redhat-1]
This error manifests due to the Portlet Bridge needing to retain the UIViewRoot from JSF between Portlet Requests, which causes the list of component tree actions, ie. adding and removing, to be retained making JSF think that it's trying to remove a component that was actually removed in a previous request.
This has been raised as http://java.net/jira/browse/JAVASERVERFACES-2609, but wanted to raise this as a tracker so that when that fix is available it can be incorporated.