Shortcut icons "disappearing" from desktop


Shortcut icons on my desktop are becoming "invisible" with increasing regularity. Most days when I start up there are one or two icons that do not show up. The text is visible and the link is still there if I click on it but I cannot see the icon.

I can make the icon visible again by Rt-Clicking on the icon, selecting Get Info and then clicking on the desktop again, but does anyone know why this is happening?
They are "Aliases." "Shortcut" is Windows parlance. The fate of your aliases are tied to the real objects that they are linked to. My first thought is that your icons are displayed as preview thumbnails. The preview thumbnail of a document with a lot of whitespace may appear to be blank.

If this hypothesis is not accepted, then you will need to post a screenshot that shows your problem.