Tibbers can't be commanded to attack inhibs [GAMEPLAY]

I've been maining Annie for a rather long time, and this question has always lingered in my mind. It always seemed more like a bug than an actual gameplay element, considering the fact that tibbers Does, infact attack inhibs if you decide not to command him to do so (When he's kinda on AI mode). Which one of these is the bug, should he be able to attack them or not? It feels a little bit strange, considering the fact that I'm pretty sure you can get daisy to do it. Thanks