I'm noticing this is happening to me a lot more than it should (It really shouldn't be happening at all), whenever I log in I always select the forever duration so I never have to log off, yet it insists that for the hell of it that I'm suddenly logged off in the middle of browsing a thread. Sometimes it happens every few hours, it happens every other day, or it happens every five minutes.
Forever is forever. Meaning: Log in once, stay logged in, I shouldn't have to log back in unless I delete my browsing history and cookies and all that good stuff, or if I intentionally log off, not whenever it feels like it.