Fiora Q targets invisible units

My friend just got out of a game with Akali where he (intelligently) used his shroud to back out after trades so she wouldn't be able to auto him but without fail her Q autotracked him regardless of visibility. Is this working as intended or is this a bug? It seems rather unfair that this skill could auto-track stealthed targets and it makes Akali about as good as Release Bard against a Fiora.