What do you have in so far as browser cookie settings? Do you have cookies set to always accept, always deny, or always ask? Do you clear your browser cache/history after you finish browsing? Do you have something set to do it automatically (some "cron" job, using fcron or alarmed, for instance)?

Anyway, I never have password set to save, because I value the extra layer of security (if a person grabs my device and goes online with it while it's not locked, they don't get in any of my accounts), and think it's sad when people are too lazy to type in their nicknames and passwords - but for places I don't log out (like here), the browser (MicroB at least) seems to remember me indefinitely. I don't think it's purely a PR1.3 bug because other people have been fine, and I'm sure you're not the only few people having your browsers sign you in automatically.

It's probably a mix of browser, and something else. *Shrug*