Exhaust bug with Darius ultimate.

Okay so recently I've been playing a lot of top lane. and I've been going Up against a few Darius's in my time. well now I've noticed a large problem and possible bug. Well Exhaust directly quoted says. "Exhaust is a targeted Summoner spell that affects enemy champions. It reduces their movement speed and attack speed by 30%, their armor and magic resistance by 10, and their damage dealt by 40% for 2.5 seconds." Now this poses a problem because while Darius's ultimate does true damage (which ignores armour and magic resist.) it should not ignore the 40% pure damage reduction from exhaust since it's damage dealt directly by one of Darius's abilities. although true damage should ignore all armour it should ignore exhaust a summoners spell that has a cooldown twice as long as his ult because it's supposed to be strong and be able to save you from being bursted down. this should also be true fro champions like Master Yi who also ignore exhaust with their abilities. (P.S Love you riot just wanted to bring this up as a side note since the new patch came out and you'll be doing bug fixes anyways.)