Custom Shortcut Weird Behaviour

Hi everyone,

I'm using Illustrator CS6 on Mac, and I set a custom shortcut for displaying slice options (Object -> Slice -> Slice Options)

And sometimes the shortcut works, sometimes it doesnt.

It is usually stop working when I copy object from another illustrator file.

And it will work again after I go to the normal place on the menu (Object -> Slice -> Slice Options). After I go to that menu, when I typed the shortcut, it will work again and it will stop again when I copy something from another place.

I tried setting a different shortcut, but it's the same.

Is anybody experiencing the same thing?

Thanks.