I am so glad someone started this post. My puppy who who turns 8 months this week and we adopted about a month ago is doing the same thing. We took him for his first walk the other day. We were so happy we didn't even have to train him on his harness, he walks like he's been doing it for a long time.
Suddenly, we were passing by a park with a couple of dogs, the owners came to say hi to my dogs and lo and behold, the smallest of my baby started barking and jumping like crazy. He is actually mean.. it was so funny. He won't stop either. So, we just walked away and he stopped.
I will definitely try the treat thing next time.