As much as I love Shaco, this isn't a bug.
Firstly, it's in place to add counterplay to his ganks (which are fearsome even with his Deceive being visible in the fog of war. A champion that's already able to elude nearly every ward the enemy can place needs at least some form of counterplay, and that is it.
Secondly, if one were to buff Shaco (which I believe he needs), this would be incredibly low on the priorities list. His Deceive being able to be seen through the fog of war doesn't really inhibit his ability to gank.
I would, however, like to see Shaco's clone start imitating buffs, weapon effects, emotes and such, better itemization/scaling, and more ways to do damage other than throw your shiv and autoattack. But I digress.