We know you can either click on the show desktop icon or use CTRL+ALT+D to ask Ubuntu to show the desktop. Unfortunately, this does not always show the desktop in one action.
Sometime, and this is true for at least the last 4 version of the OS, it brings up first to the front all the windows, THEN, with a second click, show you the desktop.
This is very annoying, as when you show the desktop it generally to quickly click on a shortcut.
To understand what I'm talking about, open 7 windows, minimize some, bring some to the front, maximize one, then show the desktop. Then do that on Windows. You'll see the difference.