Jinx Q bug

So, I was playing with Jinx the other day and found an interesting bug; using my Fishbones didn't have a minimum cost. While using Fishbones, if I ran out of mana, I was automatically switched back to Pow-Pow. That's normal, right? But I was able to switch back to Fishbones instantly. If I had less than the minimum cost I could still switch back. It used as much mana as I had and switched me back to minigun. But by mashing Q I could keep using rockets in fights.