Vista limited account desktop background changing itself to admin's desktop backgnd
 

I'm using Vista and limited account and couple times my desktop background changes itself to one I set for my administrator account. I always use a limited account and sometimes not often the desktop background would change to the one I set for admin account for no apparent reason say once every two months. It even happened twice yesterday.

Should I be worry?

Or is it one of the less advertised Vista 'feature' as the disappearing recycle bin? lol