Issue with OnAssignMaterialModel and meshes split by Unity

Hello all,

I'm having an issue where implementing my own AssetPostprocessor.OnAssignMaterialModel() method is causing an issue on models with > 64k verts. I have searched high and low with no luck, as well as posted a thread at the Unity forums, but it hasn't been responded to after a few days. The issue that I'm seeing is that when the model is split by Unity, and I use my AssetPostprocessor.OnAssignMaterialModel() method, only the last sub-mesh has the material applied. The reason I need to support models that may be split by Unity on import is because this I'm building an automated process, and mesh size upon import is not guaranteed.

If my model has less than 64k verts this code works. If there is something else I can do, short of recursing through and manually setting a shared material on all split meshes after import to account for this, I would love to hear about it. Apparently the default functionality of Unity accounts for this, so I'm not sure what I'm doing differently.

It is very possible that I'm doing something very wrong, but unless I'm missing something the documentation on this functionality is quite lacking. Any help would be greatly appreciated!

This is what my code looks like:

 Material OnAssignMaterialModel(Material material, Renderer renderer)
     {
         string materialPath = "Assets/Materials" + material.name + ".mat";
 
         //if the materials folder does not exist let's create it
         string pathToCheck = Application.dataPath + "/Materials";
         if(System.IO.Directory.Exists(pathToCheck) == false)
         {
             AssetDatabase.CreateFolder("Assets", "Materials");
         }
 
         DebugLogger.WriteToLog(DebugLogger.EDebugLevel.DEBUG_INFO, "Material.Name = " + material.name);
 
         // Find if there is a material at the material path
         // Turn this off to always regeneration materials
         if (AssetDatabase.LoadAssetAtPath(materialPath, typeof(Material)))
         {
             DebugLogger.WriteToLog(DebugLogger.EDebugLevel.DEBUG_INFO, material.name + " already exists");
             return AssetDatabase.LoadAssetAtPath(materialPath, typeof(Material)) as Material;
         }
 
         // assign the proper shader based on textures found for the material.
         string mainTexture = System.IO.Path.GetFileNameWithoutExtension(AssetDatabase.GetAssetPath(material.mainTexture));
 
         //Get the name of the main texture without the suffix
         string[] mainTextureSplit = mainTexture.Split('_');
         string mainTextureSansSuffix = "";
 
         if(mainTextureSplit[mainTextureSplit.Length - 1] == "d")
         {
             //loop through adding everything except the first split back
             for( int i = 0; i < mainTextureSplit.Length - 1; ++i)
             {
                 // add underscores back where needed
                 if(i != 0)
                 {
                     mainTextureSansSuffix += "_";
                 }
 
                 mainTextureSansSuffix += mainTextureSplit[i];
             }
         }
         else
         {
             DebugLogger.WriteToLog(DebugLogger.EDebugLevel.DEBUG_WARN, 
                                    "ImporterOverride.OnAssignMaterialModel() : mainTexture is missing or wrong naming convention!");
         }
 
         // Default the shader to Diffuse
         material.shader = Shader.Find("Diffuse");
 
         //do we have a properly named main texture
         if(mainTextureSansSuffix != "")
         {
             string bumpMap = mainTextureSansSuffix + "_n" + System.IO.Path.GetExtension(AssetDatabase.GetAssetPath(material.mainTexture));
             bumpMap = System.IO.Path.Combine(System.IO.Path.GetDirectoryName(AssetDatabase.GetAssetPath(material.mainTexture)), bumpMap);
             string specMap = mainTextureSansSuffix + "_s" + System.IO.Path.GetExtension(AssetDatabase.GetAssetPath(material.mainTexture));
             specMap = System.IO.Path.Combine(System.IO.Path.GetDirectoryName(AssetDatabase.GetAssetPath(material.mainTexture)), specMap);
 
             Texture2D textureBump = AssetDatabase.LoadAssetAtPath(bumpMap, (typeof(Texture2D))) as Texture2D;
             Texture2D textureSpec = AssetDatabase.LoadAssetAtPath(specMap, (typeof(Texture2D))) as Texture2D;
 
             // if we have both a bumpmap and specmap then we need the appropriate shader
             if(textureBump != null && textureSpec != null)
             {
                 material.shader = Shader.Find("Bumped Color Specular");
                 material.SetTexture("_BumpMap", textureBump);
                 material.SetTexture("_SpecMap", textureSpec);
             }
             else if(textureBump != null) // just bump diffuse
             {
                 material.shader = Shader.Find("Bumped Diffuse");
                 material.SetTexture("_BumpMap", textureBump);
             }
             else if(textureSpec != null) // just specular
             {
                 material.shader = Shader.Find("Specular");
                 //material.SetTexture("_SpecMap", textureSpec);
             }
         }
 
         //Add material to the AssetDatabase and return the material
         AssetDatabase.CreateAsset(material, "Assets/Materials/" + material.name + ".mat");
         return material;
     }