Braum Ult bug

I was trying to figure out how it happened and I think this is it. So I ulted before a Miss Fortune auto hit me for kill. My ult went off but my cooldown for it didn't go off. The cooldown was registered since I was able to ult again but I wasn't able to see the cooldown until I ulted again. Thats all I really have on it I hope some with a bit more experience can look into this further.