Ekko [E] and Tristana [R] unwanted interaction?

I don't know if that is intended or not since auto-attacks still hit him but when Tristana used her ultimate on Ekko while he was starting the animation for his E (the "flash" not the "roll") he ignored the damage and the knockback while her ultimate went on cooldown.

Is this intended or did i never notice it was possible to dodge on-target abilities with Ekko's E?