I realized a problem, with grouped objects in Bryce. When I move a single object of a group, somtimes it happened, that all of the objects of this group are moving suddenly, to positions I did'nt set. It seems the objects trying to get the actually position and dimension of the group that has before. Maybe this could be the reason of the behavior of the objects in your scene?

Only a thought.

Allibaba

Only 3D and Bryce, comes at my pictures!!!