XP Screen Saver password uses Old password until logout or New one is used.

["Ghazi H. Al Wadi [NGHA-CTC]" <wadig () ngha med sa>]

Hi,
Today I have as usual, changed my PC logon password (XP Home Edition). When
the screen saver started, I dismissed it and by force of habit, I typed the
old password. To my surprise I was able to unlock the screen saver using the
old password.
I  was able to do that several times, However, once I logout or use the new
password I am unable to use the old password and have to use the new one.

The question is , Is this a feature. and from a security point of view
wouldn't that be a vulnerability. If not is it documented any where. And
last, was this issue addressed before.

Kindest regards
Ghazi Al Wadi