Its a security feature of the software to stop the server being flooded by bot type activity.
If you log in and then make a post (or make 2 posts or anything that sends info to the server rather than receiving) within 15 seconds you will get that message displayed.
I have the log-in set to always remember so I never log out or in.
However, the time shown as active is only when you are actually viewing the forums
Me too.
.. and yes 'Total time logged in' is actually a bit misleading, since it only records your actual Active time on the forum.
Your session will expire even if the browser window is still open and theres been no activity for 15 mins.