Fireball Piercing at level 2

I just started the league and I went witch with fireball. As I got to the the coast from town I noticed fireball piercing. I am not sure if it is an animation bug or something else.

First cast hits does ~60% hp to white mobs. 2nd cast would randomly do its damage but not explode as the fireball pierced the target and kept going. After playing for a few more mins, I noticed that when it did pierce and eventually exploded on a brand new target, it did not do any damage.