Rudy does this too and he's also a big boy (Border Collie/Australian Shepherd/Great Pyrenees mix with more of the latter's size). I's cute and different because generally speaking, even in play, he's not a submissive dog at all. He's sort of an alpha, except with small dogs and his brother (actual littermate) that he plays with every week and who is much more passive than him. It's like he knows he needs to handle them gently.