I'm not sure how to replicate this 100% predictably yet but I can occasionally get the ACE Showcase into a state where the following NPE is thrown when the FacesUtil.getManagedBean method is called:

SEVERE: could not get value for bean panelListener
java.lang.NullPointerException
at org.apache.catalina.core.DefaultInstanceManager.processAnnotations(DefaultInstanceManager.java:460)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:146)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:139)
at org.apache.myfaces.config.annotation.Tomcat7AnnotationLifecycleProvider.postConstruct(Tomcat7AnnotationLifecycleProvider.java:90)
at org.apache.myfaces.config.ManagedBeanBuilder.buildManagedBean(ManagedBeanBuilder.java:211)
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver.createManagedBean(ManagedBeanResolver.java:332)
at org.apache.myfaces.el.unified.resolver.ManagedBeanResolver.getValue(ManagedBeanResolver.java:295)
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
at org.apache.myfaces.el.unified.resolver.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:171)
at org.apache.myfaces.el.VariableResolverImpl.resolveVariable(VariableResolverImpl.java:65)
at org.apache.myfaces.el.convert.VariableResolverToELResolver.getValue(VariableResolverToELResolver.java:116)
at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
at org.apache.myfaces.el.unified.resolver.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:171)
at org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:71)
at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
at org.icefaces.samples.showcase.util.FacesUtils.getManagedBean(FacesUtils.java:86)
at org.icefaces.samples.showcase.view.navigation.NavigationController.navigate(NavigationController.java:145)
at org.icefaces.samples.showcase.view.navigation.NavigationController.navigate(NavigationController.java:66)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.el.parser.AstValue.invoke(AstValue.java:262)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:278)
at org.apache.myfaces.view.facelets.el.ContextAwareTagMethodExpression.invoke(ContextAwareTagMethodExpression.java:94)
at javax.faces.event.MethodExpressionActionListener.processAction(MethodExpressionActionListener.java:79)
at javax.faces.event.ActionEvent.processListener(ActionEvent.java:51)
at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:371)
at javax.faces.component.UICommand.broadcast(UICommand.java:103)
at org.apache.myfaces.view.facelets.component.UIRepeat.broadcast(UIRepeat.java:1158)
at org.apache.myfaces.view.facelets.component.UIRepeat.broadcast(UIRepeat.java:1158)
at javax.faces.component.UIViewRoot._broadcastAll(UIViewRoot.java:990)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:280)
at javax.faces.component.UIViewRoot._process(UIViewRoot.java:1275)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:728)
at org.apache.myfaces.lifecycle.InvokeApplicationExecutor.execute(InvokeApplicationExecutor.java:38)
at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:171)
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:189)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:964)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:304)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:680)

This may be constrained to an app issue but it does require that the app be restarted/redeployed in order to use the particular demo that triggered the problem.