[mod_python] Session expires early

Does anyone know why, or has anyone else notices, that a session seems 
to time out reguardless of when it was last accessed?
i.e. I'm browsing along for 20-30 minutes, and then the I click a link 
after being idle less than 5 minutes, and suddenly my session is expired.

This even happend today when I was showing something to a client, on my 
laptop.