Hey again Chimp,
So I managed to look into this a bit further and discovered it is in fact a double quad overlapping one another. I also looked into the camera facing material itself and found that there are parameter values and specifics related directly with the model size and shape of those two quads.
Pine Billboard Mesh
So if you notice, there are a couple of quads intersecting, but they are extremely close to one another. If I were to zoom out, it would almost look like a line. This definitely has an effect on how the tree is rendered and adds to the camera facing effect.
I tested out your quads and was able to get the same results you were experiencing, but after all of this new information I am to the conclusion that this material is specific to the mesh they created.
You might be able to change the parameters so the material renders correctly, but I suggest using it as a guide to setting up your own custom material. This will not only ensure it works correctly, but you can learn the how and why to creating this type of camera facing material. Best of luck!
Cheers,