Apache mod_proxy, page reload and sessions

I use the apache "mod_proxy" to forward all requests to the glassfish server. The relevant apache config is:

# proxy to glassfish app 
  ProxyRequests Off
  ProxyPreserveHost On

  <Proxy *>
    Order deny,allow
    Allow from all
  </Proxy>

  ProxyPass /myAppVaadin/VAADIN/ http://127.0.0.1:8080/myAppVaadin/VAADIN/
  ProxyPassReverse /myAppVaadin/VAADIN/ http://127.0.0.1:8080/myAppVaadin/VAADIN/
  ProxyPass /myAppVaadin/APP/ http://127.0.0.1:8080/myAppVaadin/APP/
  ProxyPassReverse /myAppVaadin/APP/ http://127.0.0.1:8080/myAppVaadin/APP/
  ProxyPass / http://127.0.0.1:8080/myAppVaadin/
  ProxyPassReverse / http://127.0.0.1:8080/myAppVaadin/

The problem is the following:

If I use my Vaadin web application without the proxy then the browser page reload button reloads the current view without a new session is created. But if I use the web application with the apache proxy the page reload button creates a new session (and I must login into my application again).

Anybody knowns how I can prevent that I get a new session if I reload a web page by using the apache proxy?

Thanks and regards,
Steffen

PS: with the mod_proxy_ajp I have the same effect