Passwords being blanked when rebooting Vista

Sometimes, not every time, when I reboot or even log off/on, passwords
permanently configured in apps such as Outlook 2007, Windows Live Mail, and
Skype are blanked. I think the common denominator with these apps is that
they rely upon elements of the system shell significantly, so this is
probably related to Vista in general in some way.

I do close the mail programs before restarting, so that's not the cause.

Any ideas? It's quite annoying to have to resupply the passwords so
frequently.

Vista Premium SP1