Arcane Comet bug???

There is a bug with Arcane Comet?? I was in URF mode and I was playing against Annie, when she or Tibbers were near me, and I receive dmg, Arcane Comet would go off like 30 times all at once! There was no cooldown what so ever to it!!! Like I know it is URF and spells don't have cooldowns, but Annie literally killed me just by Tibbers standing near me?!