Challenger Smite vision issue

So I've been playing Jungle against champs that can disappear (Shaco, Rengar) and I like to take Challenger Smite when I go against them. However, when I smite them, the vision isn't granted. Which is kind of irritating see as Shaco can q away and my vision should be there, but isn't. Maybe its shorter than i expected, but I don't think its sub 2 seconds.