Not sure if it is a bug or intended. The "Riposte" tool tip says Fiora will block all incoming damage but it cannot block the damage from an enemy turret. I found it out in a custom game. Haven't tried normal or ranked games, but I assume it will be the same.
I guess you expect Yasuo's Windwall to also block turret shots?
It will not block tower shots.
I found this out myself, attempted to tower dive, wagering about 50/50 it would work. Didn't, got the kill though. I think it's intended this way though, it just blocks all non-turret things that would affect you. In fact, as I discovered, if your timing is like... reallly god tier, or you just get lucky, you can Riposte an opposing Fiora's Ult and not have any of your Vitals Revealed from it.
