My Bitcointalk account keeps logout even if I click that remember me box when I close the Bitcointalk tab and turn off WiFi.
So far I haven't run into the same issue, but if it were, I'd never feel it would be a risk. Your account will be at risk if you see a different IP, it could be that your account was recently compromised but they didn't change the password and email. This is just an assumption, but you can monitor your IP here:
https://bitcointalk.org/myips.phpAnother thing that I think is, you may not have the password auto-saved in your browser for the bitcointalk account. But for security reasons, you don't need to save it. It's better if your account logs out automatically.