OK - then that looks like a bug. As long as nothing's been modified there - and now that we've narrowed it down you'll probably need to report this as a bug over at ubbcentral.com.
I guess you could try making sure you're using the most current start_page.php (which is what sends the password). But in 6.4.1 the mail function was centralized, so it's a mystery how it works in one script and not the other, since mail is only sent from one place in 6.4.1.
So we might need the master to track this down.
Post it as a bug and give a link to this thread so he can see the specifics.
