Serialize ground probleme

I have some problem when I serialize a terrain. then the serialized data is not reloaded with ImportMesh.

As soon as there is a texture on the ground, the serialization it passes bad. The only time it works is when a texture is not added. For exemple :

With no material :

If I take the case of a simple ground with CreateGround()  it will work (Because no textures are added here) . But if I create now with CreateGroundFromHeightMap() it will not work (Here we add a texture)

http://www.babylonjs-playground.com/#1SQFJP#16

With TerrainMaterial :

If I create a terrain and use TerrainMaterial, this time neither CreateGround() and CreateGroundFromHeightMap() will not work for serialization for reloading with ImportMesh (Here we add textures with the materials)

https://www.babylonjs-playground.com/#E6OZX#191

With MixMaterial :

Same thing if I use MixMaterial instead CreateGround() and CreateGroundFromHeightMap() will not work for serialization for reloading with ImportMesh  (Here also we add textures with the materials)

https://www.babylonjs-playground.com/#E6OZX#190

Thanks