wallpaper question

I had a client ask me about this yesterday. I have seen it happen before but I have no idea what causes it or how to correct it.

On windows start up, the normal proces is that the wallpaper shows up then the desktop icons appear over it.

On his computer it started having the wallpaper come up, then disappear, then the desktop icons appear, then the wallpaper reappears behind the icons. Then some of the icons vanish then come back. The whole start up process seems to be slightly slower than before this started happening.

Is this due to other programs loading at start up? Is there a way to correct it?