three likely possibilities
1) "log out" eliminates the cookie, but some browsers have "remember this login" esque features that repopulate those cookies
2) you might be logging out on www.forums.ffshrine.org and not on
http://forums.ffshrine.org, it won't carry over from one to the other or vice versa
3) you might have more than one browser window/tab open to the same location and the second might overwrite it