A bug with Fizz's ultimate

I was playing fizz, and I reached level 13 or so. And I used my ult in a 3 v 5 against the enemy team, as soon as I threw it, I died, I didn't care much, it was what happened after that intrigued me, the cooldown didn't reset, or so I thought. I immediately tried using it again, but it didn't work for 3 mins or so, longer then the usual cooldown. anyways, I hope this can be fixed, so it doesn't affect anyone else. Thank you for reading this thread.