[user104658]

Also worth noting that the way a dog interacts with people doesn't dictate at all how they are around other dogs. My mum had a little Border Terrier who was the sweetest little soul around human beings - butter wouldn't melt in her mouth, just a silly cuddly little thing.

... ... ... she could NOT be around other dogs, and would attack on sight. She would literally go for the neck of dogs 4x her size, it was horrendous trying to walk her, and really hard to train it out of her (we were never successful) because the behaviour was only present around other dogs.