Opera 12:16 losing my Master password?

A Former User

While logging on to a site I use regularly, Opera didn't prompt me for my Master password but instead requested a new Password - without asking for my current one.

I recycled Opera (and, eventually, Windows), but whenever I tried to log on to any site for which I had saved login details, I got the same dialogue.

I then tried "Set Master Password" in "Preferences". It gave me the same dialogue, i.e. no box for entering my current password. I set the new password to my actual one. The wand then worked as usual - except that it didn't sent passwords, just the user-ids.

Fortunately my backups were current, so I restored some Opera files from 24 hours previously and everything now seems OK. So, a couple of questions, please...

(1) How do I avoid Opera "forgetting" my Master password?

(2) If this happens again, which file(s) should I restore? I actually used the following but I'm sure that that was overkill...
opcert6.dat
oprand.dat
opssl6.dat
spdysett.dat
operaprefs.ini

I'm using Windows 7. The only recent change I remember making to Opera was to install the Tab Vault 2.5.6 extension and to re-enable Ghostery.

Thanks,
Brian.