This site needs to review how it is built. Writing a post can take more time than one is allowed to be on the site without 'activity' taking place making the server think that the person is not doing anything. The server will then show the 'you need to login' page when trying to post to the forum. With the result that all that typing and putting together of the post is all wasted.
This is a programming issue not a user issue. There are plenty of PHP websites that hold the info in memory and allow one to use the back button to go back and retrieve the text that one has written even though the user has been logged out by the system.
If the excuse about security comes up, I say to you what security issue? Is this a bank? Are we dealing with sensitive info? No on both counts. If a hacker wanted to cause problems for this site s/he would do so regardless of the securty measures in place.
But for this kind of site this is pretty pathetic.
It is goddamn sloppy to timeout someone just becuase they have not been browsing posts, when in fact they are writing one. I have seen quite a few chat windows having the wording appear telling you that the 'Agent is typing'. So there is this function out there somewhere in coding land that tells the server that activity is still happening which will prevent the time-out from occuring.