The other day my friend was playing his life/fire wizard in Colossus Boulevard. He used Leprechaun and it did no damage. And the gobbler didn't have a Spirit Armor or anything! Is this a known bug?
It's possible that something happened that caused the server to show that the Leprechaun had been cast when in fact it had fizzled, or some other error may have occurred. If it doesn't happen frequently, then there's nothing to be done about it.