toggle showing desktop stumbles

Hi there. I've got <ctrl><alt>D set up as an alternate for "toggle showing desktop". I have the wallpaper set up in slide-show mode - lots of pictures. So when one comes along I like (kicker is translucent), I <ctrl><alt>D to see it. I tried holding down <ctrl><alt>D to see how quickly the desktop redraws and it flickered a few times before all the apps disappeared, after which pressing the key-combo had no effect - the desktop background was permanent. I could click on the apps in kicker to bring them back individually. Is this a bug? Regards, Philip Ashmore