IT's the intended behaviour for fiora.
ACTIVE: Fiora poises to strike in the target direction and then enters a defensive stance, parrying all incoming non-turret damage and hostile crowd control effects for the next 0.75 seconds.
http://leagueoflegends.wikia.com/wiki/Fiora
Not for nocturne.
ACTIVE: Nocturne creates a barrier** that blocks the next enemy ability** that hits him within the next 1.5 seconds. If Nocturne blocks an ability, Shroud of Darkness' bonus attack speed is doubled for 5 seconds.
http://leagueoflegends.wikia.com/wiki/Nocturne
That's why I ask for the video/gif anything of the bug ?