Annie Ult Bug [GAMEPLAY]

So I was testing out some rune pages with Annie and I noticed that I only casted my ult once and it never went back on cooldown. Really weird that this happened. The ult stayed as if Tibbers was alive, however he was not and although I tried to recast, it was as if I had no R at all. Unfortunately, I have not been able to recreate this yet but am trying to.

I have a screenshot but not exactly sure how to post it~~~~