Gragas E hitting minions and crepes that are behind him

Creeps* It's early I was subconsciously hungry for crepe.

Just went to E someone and my knock-up hit creeps that were touching my ass behind me. It seemed pretty buggy. Unless his ass is what does the knock-up?

Also new to champ, but I E'd through a wall and hit someone, but it didn't do the Knock-Up I think overall either I didn't read correctly or its bugging? It seems like something weird and incorrect happens often when I use it.. And it;s usually related to hitting minions that are around me but not in front. Possibly a collide issue?