Ejb3AuthenticationInterceptorv2.invoke() throws IllegalStateException

My web app is based on JBossAS 6, EJB 3.1, Weld, and RichFaces 4. When I'm doing just a few mouse clicks and then do nothing (i.e. waiting for a timeout), then I get the following stacktrace. I upgraded to JBossAS 6.0.1-SNAPSHOT Hudson build 2296 to have Weld 1.1.0.

ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/swe2]] Session event listener threw exception: java.lang.IllegalStateException: Local Call: Security Context is null
at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:109) [:1.7.20]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41) [:1.7.20]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67) [:1.7.20]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.ejb3.core.context.CurrentInvocationContextInterceptor.invoke(CurrentInvocationContextInterceptor.java:47) [:1.7.20]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67) [:1.0.1]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.ejb3.interceptor.EJB3TCCLInterceptor.invoke(EJB3TCCLInterceptor.java:86) [:1.7.20]
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102) [jboss-aop.jar:2.2.1.GA]
at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:333) [:1.7.20]
at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:158) [:1.7.20]
at org.jboss.ejb3.nointerface.impl.invocationhandler.NoInterfaceViewInvocationHandler.invokeEndpoint(NoInterfaceViewInvocationHandler.java:143) [:]
at org.jboss.ejb3.nointerface.impl.invocationhandler.NoInterfaceViewInvocationHandler.access$000(NoInterfaceViewInvocationHandler.java:54) [:]
at org.jboss.ejb3.nointerface.impl.invocationhandler.NoInterfaceViewInvocationHandler$1.invoke(NoInterfaceViewInvocationHandler.java:103) [:]
at org.jboss.ejb3.sis.reflect.InterceptorInvocationHandler$1.proceed(InterceptorInvocationHandler.java:84) [:1.0.0-alpha-1]
at org.jboss.ejb3.sis.InterceptorAssembly$1.proceed(InterceptorAssembly.java:82) [:1.0.0-alpha-1]
at org.jboss.ejb3.nointerface.impl.async.AsyncClientInterceptor.invoke(AsyncClientInterceptor.java:119) [:]
at org.jboss.ejb3.sis.InterceptorAssembly$1.proceed(InterceptorAssembly.java:74) [:1.0.0-alpha-1]
at org.jboss.ejb3.nointerface.impl.invocationhandler.ObjectMethodsInterceptor.invoke(ObjectMethodsInterceptor.java:78) [:]
at org.jboss.ejb3.sis.InterceptorAssembly$1.proceed(InterceptorAssembly.java:74) [:1.0.0-alpha-1]
at org.jboss.ejb3.sis.InterceptorAssembly.invoke(InterceptorAssembly.java:90) [:1.0.0-alpha-1]
at org.jboss.ejb3.sis.reflect.InterceptorInvocationHandler.invoke(InterceptorInvocationHandler.java:110) [:1.0.0-alpha-1]
at org.jboss.ejb3.nointerface.impl.invocationhandler.NoInterfaceViewInvocationHandler.invoke(NoInterfaceViewInvocationHandler.java:115) [:]
at org.jboss.ejb3.proxy.javassist.JavassistInvocationHandlerAdapter.invoke(JavassistInvocationHandlerAdapter.java:71) [:1.0.0-alpha-1]
at de.swe2.bestellverwaltung.ui.Warenkorb_$$javassist_18.toString(Warenkorb$$_javassist_18.java) [:]
at sun.reflect.GeneratedMethodAccessor318.invoke(Unknown Source) [:1.6.0_23]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) [:1.6.0_23]
at java.lang.reflect.Method.invoke(Method.java:597) [:1.6.0_23]
at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:305) [:6.0.1-SNAPSHOT]
at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54) [:6.0.1-SNAPSHOT]
at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163) [:6.0.1-SNAPSHOT]
at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:299) [:6.0.1-SNAPSHOT]
at org.jboss.weld.bean.proxy.EnterpriseBeanProxyMethodHandler.invoke(EnterpriseBeanProxyMethodHandler.java:126) [:6.0.1-SNAPSHOT]
at org.jboss.weld.bean.proxy.EnterpriseTargetBeanInstance.invoke(EnterpriseTargetBeanInstance.java:62) [:6.0.1-SNAPSHOT]
at org.jboss.weld.bean.proxy.ProxyMethodHandler.invoke(ProxyMethodHandler.java:125) [:6.0.1-SNAPSHOT]
at de.swe2.bestellverwaltung.ui.org$jboss$weld$bean-jboss$classloader:id="vfs:$$-JBossAS-deploy$swe2$ear$swe2Web$war$"-SessionBean-Warenkorb_$$WeldProxy.toString(org$jboss$weld$bean-jboss$classloader:id="vfs:$$-JBossAS-deploy$swe2$ear$swe2Web$war$"-SessionBean-Warenkorb$$_WeldProxy.java) [:]
at java.lang.String.valueOf(String.java:2826) [:1.6.0_23]
at java.lang.StringBuilder.append(StringBuilder.java:115) [:1.6.0_23]
at org.jboss.weld.context.SerializableContextualInstanceImpl.toString(SerializableContextualInstanceImpl.java:67) [:6.0.1-SNAPSHOT]
at java.lang.String.valueOf(String.java:2826) [:1.6.0_23]
at java.lang.StringBuilder.append(StringBuilder.java:115) [:1.6.0_23]
at org.jboss.weld.context.beanstore.AttributeBeanStore.attach(AttributeBeanStore.java:120) [:6.0.1-SNAPSHOT]
at org.jboss.weld.context.AbstractBoundContext.activate(AbstractBoundContext.java:75) [:6.0.1-SNAPSHOT]
at org.jboss.weld.context.http.HttpSessionContextImpl.destroy(HttpSessionContextImpl.java:76) [:6.0.1-SNAPSHOT]
at org.jboss.weld.servlet.WeldListener.sessionDestroyed(WeldListener.java:97) [:6.0.1-SNAPSHOT]
at org.apache.catalina.session.StandardSession.expire(StandardSession.java:686) [:]
at org.apache.catalina.session.StandardSession.isValid(StandardSession.java:581) [:]
at org.apache.catalina.session.ManagerBase.processExpires(ManagerBase.java:691) [:]
at org.apache.catalina.session.ManagerBase.backgroundProcess(ManagerBase.java:676) [:]
at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1314) [:]
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1599) [:]
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1608) [:]
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1608) [:]
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1588) [:]
at java.lang.Thread.run(Thread.java:662) [:1.6.0_23]