Cecil,
I'm not sure where this problem might stem from, but I can tell you that I have logged in and out of the exam simulator at least 25 times today (seriously) using multiple of my accounts and my password manager never failed me.
So I know that the simulator does not simply "forget" a password or else we would have dozens and dozens of customers with the same issue. But I really don't know what might be going on here in your case.
Open question to everyone... Is anyone else experiencing this?