Comment 5 for bug 1234665

I can confirm this too.
The shortcut only works once. I have to reboot or relog to make it work again. And then, too, it only works once before it breaks up again.

Seems to be the same issue than :
http://askubuntu.com/questions/364424/superd-key-shortcut-does-not-show-desktop-in-ubuntu-13-10
http://askubuntu.com/questions/369641/hide-all-normal-windows-shortcut-is-not-working-in-ubuntu-13-10