Hi, I came across with an annoying bug. Shortcuts with "meta" can not be unregistered.
At first I thought it was a problem with my script :/

In any case, I've created a demo so you can reproduce it:
http://jsbin.com/xajipev/edit?html,js,console,output
On it you can register/unregister 2 meta/ctrl shortcuts and compare the result/behaviour with the console.

I will review it myself if I have any time...