Yea some break up little later in the year even during the rutt. I think that its just that they are so used to spending the summer together that the small ones will still group and even have large one still around with them. I dont think you'll see mature deer together though. My brother shot a very nice mature 10pnter 150's that was followed by a buck that was with him all the time on camera. I think its pretty common where I hunt to see young immature bucks still in grouped up together along with a big one around.