Garen's Q bug when hitting nexus

There is a bug with Garen's Q, for some reason Garen doesn't seem to be able to autoattack the nexus right away with his Q activated. Sometimes it has delay, a BIG delay of a few seconds until he executes the attack, and sometimes he doesnt attack at all and you just have to wait until the Q effect wears off to perform a normal autoattack on it.

It happens to me ALWAYS, anytime i try to do a Q on the enemy nexus, no matter what. BUT, it doesnt happen with other buildings at all, its just about the nexus.

Thanks