[away3d] exception when adding a material to a SubMesh [broomstick]

[Dave]

I've constructed a SubMesh like so:

var subMesh:SubMesh = new SubMesh(subGeometry, parentMesh);

If I assign a material to the SubMesh, I get the following exception/
stackdump:

Main Thread (Suspended: TypeError: Error #1009: Cannot access a
property or method of a null object reference.)
        away3d.core.base::SubGeometry/get animation
        away3d.core.base::SubMesh/get animation
        away3d.materials::MaterialBase/addOwner
        away3d.core.base::SubMesh/set material
       <snip>

public function get animation() : AnimationBase
{
        return _parentGeometry._animation;
}

_parentGeometry is null.  This is only set in
Geometry.addSubGeometry().

When I add a SubGeometry to a SubMesh, am I also supposed to add the
same SubGeometry to Mesh.geometry also?

I suspect I'm running into a slightly underdeveloped part of the API,
and I'm trying to figure out how best to steer around this error.

I need to have one object, with multiple materials.  I'm happy to
achieve this however I can with the current API.

-Dave