In the last few versions of CAF, it is preferred to declare the managed beans via annotations on the java class instead of in the faces-config.xml file. So if are using that mode of operation, then the presence of the @ExpireWithPageFlow annotation on the java class enables the expire behavior.
For example:
@ManagedBean(name = "TestDefaultviewView")
@SessionScoped
@ExpireWithPageFlow
@DTManagedBean(displayName = "Test/default", beanType = BeanType.PAGE)
public class TestDefaultviewView extends com.webmethods.caf.faces.bean.BasePageBean {
...
#webMethods#webMethods-BPMS#MWS-CAF-Task-Engine