Screen Saver Setting Require Password Upon Resuming

I am running XP Pro, single user on my machine. My screen saver setting is to require a password upon resuming. Until a few days ago this was working fine, showing the Welcome screen. Then suddenly I am now (only upon screenaver resumption) getting the classic logon screen. The option setting in the screensaver settings window has changed and I am utterly unable to determine what changed it or how to return it to the original state.

My account settings are for Fast User Switching and to Show Welcome Screen. I am not part of a domain. In perusing some newsgroups I have found this question before, however nowhere an answer to the question how to fix it. I concluded that something I must have done (without me being aware of it) had changed this and consequently decided to use an XP test build on another machine to possibly pinpoint such an occurence through a phased approach. Much to my surprise I found the setting for a screensaver to 'upon resome, password protect' from the get-go, i.e. the very first time I logged on, so my attempt for analyis was proven unsuccessful in record time.....