Amumu Ult Icon Bug

Playing an ARAM earlier today, I found a very annoying bug as Amumu. I used my ult and died at essentially the same time, and my ult's icon then stayed in its "ready to use" state even though the ability was on cooldown. I had to ask my teammates whether my ult indicator was green on their screens to know when it was ready...

It did eventually fix itself and show the proper cooldown timer after I upgraded the ability to level 2, which I suppose "reset" the ability icon. Given the circumstances of the bug (dying and using his ult simultaneously), I don't really want to try replicating it because of the preciseness probably required to attempt. Just putting this out there, thanks for reading!