On OSI, all savages have an extra bonus attack against powerful pets including all dragons, white wyrms, and nightmares. It's fairly well known on OSI NOT to kill savages with your pets. Some of us learned that the hard way the first time savages were introduced to Ultima Online. As for your pet doing well the other night, I really don't know.... it's probably a bug actually. But all savages are supposed to have a bonus against your most powerful pets, so do NOT go hunting with them again to kill savages! It's supposed to be one of those ways to keep tamers in check and from being far too powerful.