Position 3D with Option "transform owner" doesn't work for (in MM) unreserved assemblies if you select in the viewport by selection frame. Then all selected parts are excluded whose owners are unreserved in MM. Correct would be to first check which owners should actually be moved and only then check which parts are unreserved.
With the Modify 3D command the same option works correctly. So the position command should be improved in the same way.