This looks like a bug to me.
The set up:
view = new View3D({"stats":true, camera:camera, clipping: new
FrustumClipping({minZ:10}), renderer: Renderer.CORRECT_Z_ORDER});
var light:DirectionalLight3D = new DirectionalLight3D({color:0xFFFFFF,
ambient:0.25, diffuse:0.75, specular:0.9});
light.x = 100;
light.z = 500;
light.y = 1000;
light.debug = true;
view.scene.addChild(light);
cube = new Cube({width:500, height:50, depth:1000, material:new
phongBitmapMaterial(Bitmap(_source).bitmapData, {shininess:100,
smooth:true, precision:2}), ownCanvas:true});
Run it. With the frustum clipping on you get a bunch of weirdness.
Without the frustrum clipping you get normal phong shading. It just so
happens in the application I set this up in I need to get down and
dirty with the cube so clipping is a must. Any ideas?
If you can't reproduce this let me know, I'll supply an example.