In 8.1 this setting appears to be a little bit different. I had success changing the keyboard shortcut to something I don't typically use (F12) and then setting that as a "Default" shortcut. I'm not sure what is different with Default and global but a global shortcut did not work for me.
[IMG]http://i.imgur.com/ZNTCSVc.png[/IMG]
[IMG]http://i.imgur.com/ZNTCSVc.png[/IMG]