[away3d] Mirror not working on loaded mesh?

[Wex]

Been banging my head against this for a few hours now... for some
reason when I mirror a mesh loaded from a 3DS file, it doesn't do
anything. Here's the code I'm testing with:

        var mat:ShadingColorMaterial = new ShadingColorMaterial(0x00FF00);
        var sphere:Sphere = new Sphere( { material:mat, segmentsH:6,
segmentsW:6, radius:10 } );
        sphere.x = -20;
        sphere.z = -200;
        m_view.scene.addChild(sphere);
        Mirror.apply(sphere, "x");

        var mesh:Loader3D = Max3DS.load("wall.3DS");
        mesh.x = -20;
        mesh.z = -200;
        m_view.scene.addChild(mesh);
        Mirror.apply(mesh, "x");

The sphere mirrors wonderfully, but the 3DS just shows up as normal.
I've dumped a load of trace-ouputs in Mirror.as to see if it's doing
anything, and it does reach the obj.addFace call; all the verts seem
to be mirrored as expected... so I'm at a loss at to what's going on.

I'm running v3.4.0 of Away.

Any ideas?