Fiora's Riposte can block Exhaust

Summoner spells are excepted in all other circumstances - why is Fiora an exception to that exception? There is no reason for her to be an exception. It was also a bug when Sivir, Nocturne and Banshee's Veil were briefly able to block summoner spells - who also require "right timing": so why is it not a bug that Fiora can do it?

To be fair, I think the ability should be functionally a Spell Shield/Dodge Chance hybrid - rather than the current complete immunity. Existing things that aren't blocked by either (including active dots) shouldn't be parried. I'd almost go as far as to say attacks and projectiles only - like Braum.