No BLIND after the TUMBLE

Ok so i was just playing a game as Teemo against a pretty fed Vayne and of course she was doing a ton of damage... The only way for us to get the game back was killing her, so i focussed on that. Anoying as a Teemo can be, i blinded her in a fight while she focussed me (and i am not entirely sure if the blind hit her or she she managed to get the last auto before it did hit) but she killed me, barely surviving... That was wierd and it stuck in my mind... In the fight after she focussed me again. This time i did clearly hit the blind on her before she tumbled (the ult-tumble) and killed me, continuing for a penta... I am not really sure if it is a bug or if it is supposed to be so, but i would apreciate some help on the matter^^