MacOS – Assign all desktops

I'm trying some of the tips from the Cult of Mac iTunes 11 tips blog post. I don't see Options > Assign To > All Desktops when I right click my iTunes 11 icon. Any ideas? Using OSX 10.8.2, that matters.

Here’s a nifty tip for using iTunes 11 in multiple Spaces or monitors: right click the iTunes icon in your dock and select Options > Assign To > All Desktops. Now when you use iTunes in full screen mode, you can also open the MiniPlayer separately and have it run in a different space or monitor. So you could have iTunes running full screen on your big external monitor while the MiniPlayer is on your laptop screen.