Starting from today I noticed that I get logged out from time to time at SE. It doesn't matter if I'm active or not. So normally I browse the web using Tor. Thatswhy "my" IP address changes every ten minutes and I assume that the login is connected with my current IP address. Is this true? If not what can be the reason for those logouts?
Logins are not associated with IP addresses in any way. I expect something in the proxy layer is interfering with your cookies somehow.
My ISP has dynamic IPs and my IP changes every few days (more if the router has spasms) but I'm not logged out.
They might do a whois on the IP to do an ISP or country-check but it's quite a lot of work for a relatively small problem.
It's more likely that your cookies are getting invalidated at some point or their servers just don't like you and keep dumping your session.
I am logged in on my netbook via wireless and even I move around between different locations with totally different IPs and domains, I always stay logged in. It must have something to do with session management of your browser or the effect that tor has on it.