In case your vet isn't one who believes in cocker rage...and just because it might be helpful.
It ultimately doesn't matter why the behaviour is occurring it's whether it's manageable or not, if it's not, it's not.
As to "fault" here's what my behavioural specialist (she's a vet, not a trainer) says...
Unless you've grossly mistreated or trained your dog to bite, it isn't your fault. Dogs develop behavioural issues like that because there is something wrong with them, physically or mentally, yes environment will have played a part but without abuse, neglect or encouragement from you that alone won't have caused it so it's not your fault.
It was about my dog, but, I think it's useful in general because with mine if I keep that in mind I can go, could I have done things differently? Yes, of course I could...but would it have made a difference? No, not really - any mistakes I might have made should never ever resulted in the extent of behaviour problems my dog has.
In your case, healthy well adjusted dogs don't bite their owners in the situation you're describing...so even if a different training method might have been a bit more succesful or you could have handled differently, those alone aren't enough to cause that, your dog has to have something wrong to start with.
That helps me anyway, I hope it is a bit useful.
And sorry about your rubbish day...