The problem is, there are two keyboard settins. the one from gnome, just called "Keyboard", available in mint menu and synapse. But if you open cinnamon settings, in there you will find "Keyboard". You go in it and it's a "cinnamon settings - keyboard" you can have different shortcuts assigned to both. it's quite confusing.
Dell XPS m1330 w/ LinuxMint13 kernel3.2.0-30-generic (x86_64) Cinnamon 1.6