Version: (using KDE 3.5.9) Installed from: SuSE RPMs This window is a special case because it always appear (by definition) having in background not responding app. So if user chooses "do not close", this window disappear and normally the region taken while ago by this window would be repainted. In this case it is not. So for example I have situation with frozen Konqueror, this window "app is not responding" I chose "do not terminate" and... I have frozen Konqueror with this window. _I_ know that this window vanished, and what I see is just not updated canvas, but regular user does not know that and keep pressing "do not terminate" or then she/he changes his/her mind and presses "terminate" which is nothing more than few color pixels now.
made summary more precise
in case of no desktop effects it's the task of the app to repaint, which cannot work as it is frozen. in case of desktop effects kwin will just repaint the area as the last pixmap is still valid.