Garbage on empty KDE desktops

[Timothy Murphy]

I am running Fedora-9 (updated) with KDE on a ThinkPad T43.
I have 8 desktops.
I find that those among them that are empty
all have the same messy screen,
with what looks like the garbled remains of an application.

Does anyone else find this?

Is there any program that will clear a desktop not in use?
Or is there some setting I can make that does this?

Any advice gratefully received.