Bard Urf Bug

I was playing urf as bard and i flashed. and it went on the full 300 second cooldown. i waited til it came back up and used it again and it was only on a 60 second cd. so idk what happened. it only happened that one time all game but i just thought ppl should be aware. anyone else get this bug? maybe on a different champ. idk maybe its just for bard