This is absolutely normal and nothing to worry about. We are in the act of choosing pecking order, and the Boston is asserting himself and saying "Look, I've been here longer, I don't know you, but I am the Alpha dog and don't forget it". As soon as the boxer either submits and says okay, be the alpha do OR fights back and says not you, buddy, I'm Alpha you'll be okay.
The situation in my household is totally opposite. The Cavaliers are so docile that they never even discussed among themselves which would be the leader. Then I brought in this strong-willed, smart talking little shihtzu who thinks she is going to be Alpha dog over everybody and everything in the house - including me and Bubba! No mounting (that I've seen!) but I've never had such a dog. She knows that she has me wolfed (just like my African Gray does),but she isn't quite sure what Bubba might do to her. I've spent the past few days working very hard on helping her understand that she is not at the top of the pecking order and needs to learn her place!
Good luck, Dan. It'll all work out and probably sooner than you think.

Critter
