Malzahar passive bug

So as I was playing malzahar, as you all know, when his next spell will summon a voidling, he receives this glowing animation that's right below where he's standing. But sometimes even after the voidling is summoned, the glowing thing stays. This usually ends up confusing me whenever I go in to fight thinking my spell will summon a voidling although I still need to use more than one spell. So I believe this is either a bug or I don't understand malzahar 's passive even though he's the first champion I've ever purchased.