Show desktop keyboard shortcut doesn't work
Create a test user account on your Mac. Adjust this same setting. See if it works. If it does, I recommend moving the following file on your user account to the Trash:

~/Library/Preferences/com.apple.symbolichotkeys.plist

Then log off &amp; back on. This will reset all Keyboard Shortcut settings back to default. If it doesn't fix it or causes other issues, simply drag the .plist file back to its former location.