Problems with session timeout with tomcat above version 6.20

Hello all!

I'm in trouble.

Here I have some applications that uses icefaces1.8.2 (jsf2, facelets and templates) and tomcat. I'm using the single sign on and realm for security and access. The login is done using a form and all works fine on tomcat version 6.20.
But in all other versions above that (like 6.26 and also version 7) the session of my applications expires ALWAYS after the time set in web.xml even if the user is using the application! In other words if I set session to 5 minutes then after 5 minutes that the session was created (user logged in) the session expires, not after 5minutes of innactivite.
Another point is if I'm using BASIC authentication then the session works normally.

Could someone help me? Maybe a sugestion? I have not found anything about this on internet.

Thanks!