I do not know why this happens but I had the same problem with KDE in Suse 9.2. The only work around that I came up with was to right-click on the desktop and create a new folder. Refresh did not work for me either. This should do it, but it is annoying to make a directory just to see the files you put there.
Well.... creating a new folder on the desktop does not help any. I tinkered with this all weekend, and nothing seems to fix the problem. No matter what application I use to place files on the desktop - file manager, web browser etc., they are never shown unless I restart KDE, or I open a file manager and browse to the desktop. I have a second computer with an almost identical install of 10.0, and there are no problems with dropping files on the desktop. They show up immediately... no refresh needed... everything works like I expect. No one else have this odd problem with 10.0? C.