check this out...
https://www.youtube.com/watch?v=KyagKzvJwYw
Very instructive!!!
When he rearranged the weight for the second run, he did two things: he decreased the weight on the tongue somewhat but he also dramatically shifted the weight to the ends. Increasing the polar moment of inertia is the physicists term for this.
Not sure which affected the instability more: the lighter tongue weight or the increased polar moment of inertia, but whatever it was it was rather dramatic.
david