I've just noticed that it's impossible for me to log out. I click the link, I choose "yes, I do want to log out," and I get the message that cookies are cleared, and it looks as if I'm logged out. When I click anything, I'm logged in again.
Sounds like your browser cookies could be corrupt. Try deleting them for UE and seeing if that helps...
It worked. I can log out and log in as often as I want now.