Taskbar iconized folder buttons show the wrong little icon

I have an annoying problem with Vista's taskbar buttons and iconified windows not showing correct window miniatures anymore for drives, special folders with azure-green icons like Music, Documents etc., e.g. http://f.imagehost.org/0502/Immagine.jpg
Once I enter Documents\mydir for example the icon in the taskbar for that folder turns like that in the image instead of reflecting the folder mini-icon you're in at that moment!

There is nothing on the net about this kind of problem! I've Googled for hours!
Hope someone can help me to find and reset the correct key(s) in the registry.

This bug has been confirmed by other users and also after a clean install from MS DVD disks. It's a (minor) bug and has been reported to MS.

Here is how it should look like: http://f.imagehost.org/0269/Immagine.jpg
Here is what happens after a while: http://f.imagehost.org/0502/Immagine.jpg and the system starts using instead this ugly yellow folder+green arrow icon for all folders: :eek:

This little bug has not disappeared even after SP2...