Overly friendly--wrong signal

Our 2-year-old labradoodle has developed some fear-based aggression with other dogs. The thing is he is extremely well socialized and loves dogs he knows. The behaviorist says that he has a good set of dog calming signals but is afraid of unknown dogs and so acts tough if they get into his comfort zone. I wonder if this is a result of his puppy-too friendly personality. He used to charge up to every person and every dog he met (if off leash) He would jump or mouth the people. Thankfully he is over that now. He also used to charge up joyfully to every new dog he met. a younger labradoodle we know (1-year-old) does the same charging in your face thing. I think the charging at other dogs can put them off and scare them. The result is that more than once, another dog has tried to put him in his place. Now he has decided that unknown dogs are bad news if they come to close to him and need to be scared off or worse. Needless to say, we have had to give up our off-leash walks and keep him away from unknown dogs. Does anyone have any experience with this problem? It is so sad to have our dog who used to love everyone now have this problem with dogs he doesn't know.