Teemo Blind can not defeasance Fevor of battle

Im not sure this is bug or not. But it is feel odd as playing. When i was against gnar in lane. I was teemo and blinded him. their was no minion. And he had no thornmail. I am sure he was blinded , because his w didnt stack. But his AA did dmg to me. At that fight he had Fervor of battle. So i suppose it is the reason. If it is not bug just ignore please. Thank you.