root screen doesnt appear when I switch to root in KDE

Have a problem switching to root from normal KDE. Am Running SuSE 9.1 and generally works well. From the normal user I sometimes need to change to root to install software etc. So, I 'switch user' from the KDE menu. Instead of getting the root screen I get YAST appearing. It used to 'switch' to root and I don't know of anything that has changed recently. Any ideas someone please..... Phill