I started using a new Chromebook today and noticed that it logged me off, as it often happens, because I had not selected the "keep me logged in" (or whatever it's called) checkbox in the home page. This happened once and I couldn't log back in, I was actually redirected to the sign-up page after entering my username / password. I guess the page thought I was trying to create a new account because it kept saying that usernames need to be unique. I got around this by opening one of the threads then clicking on the "Watched Threads" link, which took me to the login page with no issues. Not sure what that was all about, but it was funky there for a while. I can try to recreate if it would help.