The warning messages go to the server log if a facesMessage is queued. See the Text Entry example in compat-showcase. If you enter any password < 6 characters in length and exit the field, the facesMessage should be enqueued, but the following message displays in the server log:-
Dec 15, 2009 1:35:31 PM com.sun.faces.renderkit.RenderKitUtils renderUnhandledMessages
INFO: WARNING: FacesMessage(s) have been enqueued, but may not have been displayed.
sourceId=iceform:TxtPw[severity=(ERROR 2), summary=(Enter no less than 6 characters), detail=(Enter no less than 6 characters)]
Dec 15, 2009 1:35:35 PM com.sun.faces.renderkit.RenderKitUtils renderUnhandledMessages
INFO: WARNING: FacesMessage(s) have been enqueued, but may not have been displayed.
sourceId=iceform:TxtPw[severity=(ERROR 2), summary=(Enter no less than 6 characters), detail=(Enter no less than 6 characters)]
If you exit the field and go to another, then come regain focus, the warnings again appear in the server console.

Occasionally, the following exception has appeared (inconsistent--unable to reproduce more than once):-
INFO: WARNING: FacesMessage(s) have been enqueued, but may not have been displayed.
sourceId=iceform:TxtPw[severity=(ERROR 2), summary=(Input is required), detail=(Input is required)]
javax.faces.application.ViewExpiredException: viewId:/showcase.jsf - View /showcase.jsf could not be restored.
at com.sun.faces.lifecycle.RestoreViewPhase.execute(RestoreViewPhase.java:212)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.RestoreViewPhase.doPhase(RestoreViewPhase.java:110)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:310)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
at java.lang.Thread.run(Thread.java:619)