Dogs can bite the owner sometimes when they are in rage. That's very much on the hormonal/instinctual level for them and it's hard for them to distinguish whom they are biting. It's one of the dangers dog trainers/owners have to deal with. I know because i was a dog trainer for 2 years back in russia, after getting an eastern-europen shepherd. I once got beatten on my ass by Barmy before he had time to calm down. I didn't train him protection very much, although whatever he knows proved usefull many times.
Oh and overall Barmy is one of the frendliest big dogs i've known. He is seven years old now but still acts like a puppy.