Dr. Mundo E applying first hit damage throughout duration

I've been playing Mundo lately, and a few days ago I noticed his E isn't working at is was prior, and isn't doing what the tooltip says it does. I'd guess it was an undocumented buff to him, but the damage his first auto after activation should do (headbutt animation and all) _randomly _ applies on further auto attacks. If I had to guess I'd say it happens about 80% of the time. As a Mundo main, I'd love for the bug to become a full change, but right now it is annoying to farm with now and then. And we all need to see more of the Doctor's headbutt animation anyways.