confused over behaviour

hi
i have 3 dogs a springer spaniel male and 2 female sister bullmastiffs , i had the first bullmastiff at 4 weeks old but her sister came along at 4 and a half months her names star .
Star is like a gentle giant who loves cuddles ,playtime and treats and loves seeing new people although i do introduce them slowly anyhow , Shes never gone for anyone except her breeder , He's a friend of the family and to be honest i couldn't see him as a cruel owner ,Stars seen him many times sinse shes been with us , Shes 2 and a half now but each time she see,s this guy she bares her teeth and tries biting him , Could he have been cruel to her or do you think she might just not like him at all , I'm a bit confused why she acts like she does towards him .
All dogs are nuetured.
Any ideas would be greatful :)
thanks
Carol

She may associate his scent with something unpleasant that happened to her while she was with him - cruelty by him, or a painful scuffle with one of the dogs he still has. I'd just keep her on a leash when he's around, so you have more control.

There is something about him that she just doesn't like - its the same as when there are just some people that you can't take to. They don't necessarily have to have done anything to warrant it, you just don't like them.

As you are aware of this trait its best to warn him and keep her under control when he is around.

I had a situation that was similar that happened with Koko. Koko is a Retriever Mix that loves everybody. I had never seen her show an signs of not liking anyone. We were at a local dog event called Doo Dah day. This is an event to raise money for local shelters and an all around good time. There are thousands of people and dogs in a 10 block park area where the event takes place. We were sitting on the grass waiting for a concert to start when Koko started growling and showing teeth. I looked up to see an older man and a young boy walking by. She was looking in their direction. I didn't think much of it because she soon calmed down. Two hours later she did the same thing. We were in a different part of the park but when I looked up the same man and boy were walking by. I have never figured out what it was about the people that she didn't like but something about them really set her off. She had not done this before that day and she hasn't done it since. :confused:

thank you
maybe he wasnt cruel to her in any way it realy made me wonder though at first ,id hate to think anyone i knew was like that ,he owns a few dogs and the mother dog he had passed away last year with heart trouble , each time he visits when shes there shes put in another room as she keep going for him , sure does worry me as shes a large dog to be biting :(
thanks once again.
carol