Passivating-scoped SFSB fails to deploy if not implementing java.io.Serializable

10:32:47,568 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-1) MSC00001: Failed to start service jboss.deployment.unit."weld-pastecode.war".WeldService: org.jboss.msc.service.StartException in service jboss.deployment.unit."weld-pastecode.war".WeldService: org.jboss.weld.exceptions.DeploymentException: WELD-000072 Bean declaring a passivating scope must be passivation capable.  Bean:  Session bean [class org.jboss.weld.examples.pastecode.session.PostTracker with qualifiers [@Any @Default]; local interfaces are [PostTracker]
        at org.jboss.as.weld.services.WeldService.start(WeldService.java:83)
        at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA.jar:1.0.2.GA]
        at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA.jar:1.0.2.GA]
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_30]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_30]
        at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_30]
Caused by: org.jboss.weld.exceptions.DeploymentException: WELD-000072 Bean declaring a passivating scope must be passivation capable.  Bean:  Session bean [class org.jboss.weld.examples.pastecode.session.PostTracker with qualifiers [@Any @Default]; local interfaces are [PostTracker]
        at org.jboss.weld.bean.SessionBean.checkType(SessionBean.java:327)
        at org.jboss.weld.bean.AbstractBean.initializeAfterBeanDiscovery(AbstractBean.java:145)
        at org.jboss.weld.bean.AbstractClassBean.initializeAfterBeanDiscovery(AbstractClassBean.java:230)
        at org.jboss.weld.bean.SessionBean.initializeAfterBeanDiscovery(SessionBean.java:191)
        at org.jboss.weld.bootstrap.ConcurrentBeanDeployer$5.doWork(ConcurrentBeanDeployer.java:126)
        at org.jboss.weld.bootstrap.ConcurrentBeanDeployer$5.doWork(ConcurrentBeanDeployer.java:123)
        at org.jboss.weld.executor.IterativeWorkerTaskFactory$1.call(IterativeWorkerTaskFactory.java:60)
        at org.jboss.weld.executor.IterativeWorkerTaskFactory$1.call(IterativeWorkerTaskFactory.java:53)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) [rt.jar:1.6.0_30]
        at java.util.concurrent.FutureTask.run(FutureTask.java:138) [rt.jar:1.6.0_30]
        ... 3 more

10:32:47,786 INFO  [org.jboss.as.server] (management-handler-thread - 4) JBAS015870: Deploy of deployment "weld-pastecode.war" was rolled back with failure message {"JBAS014671: Failed services" => {"jboss.deployment.unit.\"weld-pastecode.war\".WeldService" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"weld-pastecode.war\".WeldService: org.jboss.weld.exceptions.DeploymentException: WELD-000072 Bean declaring a passivating scope must be passivation capable.  Bean:  Session bean [class org.jboss.weld.examples.pastecode.session.PostTracker with qualifiers [@Any @Default]; local interfaces are [PostTracker]"}}
10:32:47,816 INFO  [org.jboss.as.jpa] (MSC service thread 1-3) JBAS011403: Stopping Persistence Unit Service 'weld-pastecode.war#pastecodeDatabase'
10:32:47,817 INFO  [org.hibernate.tool.hbm2ddl.SchemaExport] (MSC service thread 1-3) HHH000227: Running hbm2ddl schema export
10:32:47,849 INFO  [org.hibernate.tool.hbm2ddl.SchemaExport] (MSC service thread 1-3) HHH000230: Schema export complete
10:32:47,876 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-2) JBAS015877: Stopped deployment weld-pastecode.war in 89ms
10:32:47,882 INFO  [org.jboss.as.controller] (management-handler-thread - 4) JBAS014774: Service status report
JBAS014777:   Services which failed to start:      service jboss.deployment.unit."weld-pastecode.war".WeldService: org.jboss.msc.service.StartException in service jboss.deployment.unit."weld-pastecode.war".WeldService: org.jboss.weld.exceptions.DeploymentException: WELD-000072 Bean declaring a passivating scope must be passivation capable.  Bean:  Session bean [class org.jboss.weld.examples.pastecode.session.PostTracker with qualifiers [@Any @Default]; local interfaces are [PostTracker]