SceneSerializer: rotation.asArray is not a function

Hello

I am trying to serialize the scene with

BABYLON.SceneSerializer.Serialize(scene)

 and am getting a "mesh.rotation.asArray is not a function".

Serialization works fine when meshes are not rotated.

On further exploration, I realised that that mesh.rotation was not a Vector3 object but an object with getters, setters and __op__: Observer. Could this be the issue? 

Can you please help me fix this.

Please let me know if you need more details.

Thank you