Once a year you might do a standard update and find it wants to remove hundreds of files that make your kde run. I've always waited a day, but today I was in a perverse mood and said yes.
It destroys your desktop, and when you try to do a console reinstall, it can't find anything. This is a result of your Debian mirror going nuts when it is receiving new updates. It takes half a day to work again. Then you just reinstall your kde.
Better still, just ignore it for a day. :)