Combine objects Instancing Materials issue

Hi, the code bellow works perfectly, however the materials become instanced not shared, am I just being silly, i can't see why or how to solve it:

P.S Nice piece of code, however I plan to tidy it and optimise so be careful

Code (CSharp):

1. private void combineMeshes(GameObject _GameObject){
2.         MeshFilter[] meshFilters = _GameObject.GetComponentsInChildren<MeshFilter>();
3.         CombineInstance[] combine = new CombineInstance[meshFilters.Length];
4.         int i = 0;
5.         ArrayList materials = new ArrayList();
6.         ArrayList combineInstanceArrays = new ArrayList ();
7.         Matrix4x4 myTransform = _GameObject.transform.worldToLocalMatrix;
8.         while (i < meshFilters.Length) {
9.             if(meshFilters[i].renderer.enabled){
10.                 MeshRenderer MFmeshRenderer = meshFilters[i].GetComponent<MeshRenderer> ();
11.                
12.                 for (int s = 0; s < MFmeshRenderer.materials.Length; s++) {
13.                     int materialArrayIndex = Contains (materials, MFmeshRenderer.sharedMaterials [s].name);
14.                     if (materialArrayIndex == -1) {
15.                         materials.Add (MFmeshRenderer.sharedMaterials [s]);
16.                         materialArrayIndex = materials.Count - 1;
17.                     }
18.                     combineInstanceArrays.Add (new ArrayList ());
19.    
20.                     CombineInstance combineInstance = new CombineInstance ();
21.                     combineInstance.transform = myTransform * MFmeshRenderer.transform.localToWorldMatrix;
22.                     combineInstance.subMeshIndex = s;
23.                     combineInstance.mesh = meshFilters[i].sharedMesh;
24.                     (combineInstanceArrays [materialArrayIndex] as ArrayList).Add (combineInstance);  
25.                 }  
26.             }
27.             // if(meshFilters[i].gameObject.name=="Wall_E" || meshFilters[i].gameObject.name=="Wall_S" || meshFilters[i].gameObject.name=="Wall_S" || meshFilters[i].gameObject.name=="Wall_S"){
28.             meshFilters[i].gameObject.active = false;
29.             //}
30.             i++;
31.         }
32.        
33.         _GameObject.AddComponent("MeshFilter");
34.         MeshFilter meshFilterCombine = _GameObject.GetComponent<MeshFilter>();
35.         Mesh[] meshes = new Mesh[materials.Count];
36.         CombineInstance[] combineInstances = new CombineInstance[materials.Count];
37.         for (int m = 0; m < materials.Count; m++) {
38.             CombineInstance[] combineInstanceArray = (combineInstanceArrays [m] as ArrayList).ToArray (typeof(CombineInstance)) as CombineInstance[];
39.             meshes [m] = new Mesh ();
40.             meshes [m].CombineMeshes (combineInstanceArray, true, true);                  
41.             combineInstances [m] = new CombineInstance ();
42.             combineInstances [m].mesh = meshes [m];
43.             combineInstances [m].subMeshIndex = 0;
44.         }
45.         // Combine into one
46.         meshFilterCombine.sharedMesh = new Mesh ();
47.         meshFilterCombine.sharedMesh.CombineMeshes (combineInstances, false, false);
48.         foreach( Mesh mesh in meshes )
49.         {
50.             mesh.Clear();
51.             DestroyImmediate(mesh);
52.         }
53.         if(meshFilterCombine.sharedMesh.vertexCount>0){
54.             // Get / Create mesh renderer
55.             MeshRenderer meshRendererCombine = _GameObject.GetComponent<MeshRenderer> ();
56.             if (!meshRendererCombine){
57.                 meshRendererCombine = _GameObject.AddComponent<MeshRenderer> ();  
58.             }
59.             meshRendererCombine.castShadows=false;
60.             meshRendererCombine.receiveShadows=false;
61.             //                // Assign materials
62.             Material[] materialsArray = materials.ToArray (typeof(Material)) as Material[];
63.             meshRendererCombine.materials = materialsArray;
64.  
65.             //                // _GameObjecttransform.gameObject.active = true;
66.         }else{
67.             DestroyImmediate(_GameObject);
68.         }
69.     }