Now that's a good observation. I have this ideal in my mind that with a bike in the workstand the front wheel should show a strong pendulum effect, swinging back and forth over the heaviest spot in the wheel for quite a while. I've got some wheels that do that. As often as not I find that it's because I didn't adjust the cones properly. New hubs almost never do it when properly adjusted. Sometimes after the races are worn in it happens.