I'm trying to export an FBX with blendshapes for use in Unreal Engine 4, and although the vertex deformation is getting exported correctly, the corresponding normal blending is not happening - the mesh is retaining the normal information from the first frame of the animation.

I've attached a hip file which shows a very basic setup illustrating the problem. As you can see, in Houdini, the normals are being correctly blended - if you scroll from frame 0 to 100 you can see the normals changing from the first blendshape to the second one.

However, no matter how I try to export this, when I bring it into any other piece of software (Modo, Maya, UE4) there is no blending of normal information.

I've tried having the normals as vertex normals, point normals, and both at the same time, but it makes no difference.

What is the correct way to get blendshapes to carry normal information for use in other software?