[GAMEPLAY] Gragas' Barrel Roll stuck on waiting for explosion

I was playing Gragas earlier since it was on free rotation, and I was stunned(?) just as I was using Barrel Roll, resulting in no barrel being thrown, but the ability was waiting for it to explode. After this, I could no longer use the skill. I don't have step-by-step instructions to reproduce, nor do I play Gragas enough to know how frequently it occurs.