One theory is that it has something to do with the engine configuration and rotation of the crank shaft. I don't know, but it's a not uncommon complaint. Checking the engine bolts is a good idea, but I also noticed that the bear claw was making me sit a little to the left of centre and the bike did what yours does. Ensuring my weight is centred, fixed it. Some have also suggested that uneven weight in saddle bags can cause it but it seemed too much of a coincidence that everyone had overloaded LHS saddle bags - but worth checking that too. As far as I can tell, Rockets just seem to do it, as it occurs in Oz and well as US, which means it has nothing to do with crown of the road.