[Gameplay] Teemo blind not working

I was playing a game as Teemo top against a Nassus. During the first 10 minutes or so of the game i would blind Nassus and the blind would be delayed so it would occur after i hit him, and then he would q something despite me having cast the blind (this means that the indicator above Nassus that says he is blind would come up anywhere from half a second to a full second after my blind hit him). After that point Nassus could use his q to hit things, including me, while the blinded indicator was active above him, i would blind him and Nassus would q me right afterwards anyway, and i would still take the damage.