In latest versions, show desktop applet cannot be used as a shortcut. To reproduce: add show desktop, create a shortcut. Sorry if this is in a wrong place.
I can confirm this bug with Plasma 5.7.1 on Fedora 24. Setting a keyboard shortcut for "Show Desktop" widget on the panel has no effect. However, if I go to System Settings > Shortcuts > Global Keyboard Shortcuts > KWin and assign the shortcut to "Show Desktop" item, it works. PS: I think it might be wrong to assign the bug against "kdeplasma-addons". Somebody please change to the right product.
I can confirm this with Arch package.
I can see why. I'll have a look.
Git commit 570d08e59f5c59dca385b2384c2e2e05e638b7d4 by Kai Uwe Broulik. Committed on 20/08/2016 at 21:10. Pushed by broulik into branch 'Plasma/5.7'. [Show Desktop applet] Fix showing desktop through applet keyboard shortcut FIXED-IN: 5.7.4 M +1 -1 applets/showdesktop/package/contents/ui/main.qml http://commits.kde.org/kdeplasma-addons/570d08e59f5c59dca385b2384c2e2e05e638b7d4
*** Bug 368271 has been marked as a duplicate of this bug. ***