Nautilus Ult CD bug

I was dueling a renekton under tower as nautilus and used my ult to keep him there. He killed me before my ult had hit him. When I was up, the icon for the ultimate was not showing that it was on cooldown. I assumed my ult never went on renekton and when I had attempted to use it again, it was in fact on CD despite not showing. Once I was able to use my ult again, it did show it on CD, but it really screwed with my engage. My teammates also saw that my ult was up when looking at my icon above the mini-map. Must've been a visual bug because when I downloaded the replay, spectator mode shows my ult on CD. Would be great to get it resolved!

Thanks!

Mister BriGuy