Why are my karate punches more like boxing punches when I hit shields and bags?

These questions were once put to me by a Shotokan karateka: "I would just like to ask your opinion. When I use the kick shields, the kick take the same form on the shields as they do in fresh air. However, whenever I use the focus mitts or bag. I seem to use more of a boxing style punch. By this I mean. jabs, straight right/left, and hooks. Now I know we can call them kizami-zuki, gyaku-zuki and mawashi-zuki. But its the way in which I strike the pad. Using the shoulder, plenty of hip and up on the balls of my feet. Also I breath through my nose. I feel very comfortable in striking this way and I can hit the pads/bags quiet hard. However, this is contradictory to the way I train and teach karate punches. Shoulders down, using the back muscles. Same hip movement, but heel down pushing to the floor. And breathing through the mouth. We do have access to makiwara. The Goju-ryu boys use these all the time. I have used one in the past, only for a short while. I do not use one now becaus...