[troyb]

this actually isn't due to something as simple as an "autocomplete=off" setting. The vBulletin folks designed the software to hash the password and remove it from the form submission when you click the log in button. This means your browser doesn't know you've entered and submitted a login / password for saving. Chances are you'll see this same thing on all vBulletin based forums.

Sorry for the inconvenience here.