life time of log-in

Gents, I am using BETA 4 and encountered the following problem: Once logged on there seems to be an inactivity period, which forces a log out w/o warning. The editor for an entry is open, accepts entries but once you want to save what you edited and you took a break of > 10 minutes in between, everything is gone. On the other end with previous betas, I could leave the xwiki for hours go to different URLs, and go back to the Xwiki and I was still logged-on. What are the policies here and IMHO both cases described above should not happen. Thanks Uwe