If your field tips are the same weight as your broadheads, my guess is that you are doing something different when you shoot broadheads. Perhaps you are thinking about shooting broadheads, rather than just thinking about shooting arrows. I know that happens to me, and my solution is to just shoot a lot of broadheads until my mind gets off the subject.
Just for fun, though, if all your broadheads are oriented in a particular direction (vertical or horizontal), you might try switching to the other orientation to see if that makes any difference.