thanks for the links.
there is something called precession. I have been wondering if the angle of the steering head, and precession, keep the bike "stable". but the experiments you posted sure make sense in showing it does not matter.
Something worth reading -
Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia
the section on Wobble or Shimmy
I'm old and fat, and was more of a snowmobiler then a motorcycler. Did your wobbles start when you let go of the handlebars because you were not hanging onto the handlebars any longer?
Perhaps there is a harmonic with the flex of the front steering system and the mass of the system - change the mass, and things quit wanting to "vibrate".