Are the middle two nails of his paws especially worn down and sort of misshapen? At my clinic, we saw a male Labrador, about 1 year old, who walked similar to the way you described. Both vets in office immediately noticed it and referred the owner to a neurological specialist. They told me that it is not a totally unusual occurence and that it is indeed a neurological problem. Since the brain is so complex and it doesn't sound like they've done extensive testing in that area, I wouldn't be so quick to rule out noggin problems. The behaviors you're describing are quite disturbing and, to me, they signal a problem more complex than a stomach ulcer.

Does she live near any major university? A university would be a greyt place for a referral. Good luck to your sister and Ben *hugs*