valueUnBound(....) methods is not called when i stop Tomcat Server or Servlet

[Nwalal mi Nyom]

Hi,
I use Tomcat4.0.1,Apache1.3.22.
in my servlet file i use class which implements HtppSessionBindingListener and I have 
implement valueBound(....) and valueUnbound(..) methods.

 when i load my jsp  valueBound(... ) is called correctly
But when l close my servlet  or  when i stop Tomcat Server,  valueUnbound(...) method  
is not called 

can somebody help me 

Thanks

Martin