A couple of people have had this..... see here
http://www.bushcraftuk.com/forum/showthread.php?t=25797
Ther server clock doesnt change as far as i know.... its the forum software that calculates local time and displays it, so make sure you check your options in your user CP and make sure they have been saved.
If you are still having problem, please post on the thread above with all your details (os, brower etc...) the more info the admin have, the better chance of tracking it down.... especially if it is only happening with a certain browser for example.
Ed