I don't know if this makes a difference, but when logged out, try logging into the forum (/vbullet/), without going to the website first.
I haven't had to login in weeks... But at the website I'm logged out all the time, because the website modifies the forum profile at every visit.
EDIT:
I confirm that visiting the forum from the website frame logs me out and in again, overwriting the profile. My solution since long ago is not to log into the website ever (unless I need to do updating). As long as I don't, my nice vbullet login persists forever. I stopped playing the quiz because of this--and it doesn't work half of the time anyway.
No further comment...
