Infinite Ferocity Rengar Bug

I played Rengar today and I stumbled upon a bug on him, after I ulted, I got infinite ferocity. Which was unfair to the enemy team. I asked them how to fix it and they suggested to make me kill my self, I did and it fixed. Well the bug happened after I ulted or some fight, I dont remember, but I suddenly could spam Q W E and it was hilarious. Without any cooldowns of course.