Resources are shared between Scene instances even when "local to scene" is checked

Question

I have the following setup:

res://Blocks/Rock.tscn:
    |-MeshInstance3D (both mesh and material come from rock.res)
        |-StaticBody3D
            |- CollisionShape3D

My levels consist of different blocks (no not minecraft) and the levels are generated in code. I instantiate and place each block like this:

var block = blockList[blockId].Instantiate<MeshInstance3D>();
_levelNode.AddChild(block);
block.Position = new Vector3(j, 0, i);

So at this point, I know that if I have say 10 of the same block, they all share the same Material. I realize it's probably not a good idea to have separate materials for each block, but for testing purposes I'd like to do it anyways. So I open res://Blocks/Rock.tscn, navigate to the MeshInstance3D -> Surface 0 -> Material and tick off Local to scene. I then save the scene file and rerun.

I'm expecting each block's material to behave independently. When I try to set Mesh.GetSurfaceMaterial(0).EmissionEnabled to true, all the blocks become emissive.

I also tried setting all the resources in Rock.tscn to Local to scene and no dice.

I even tried doing:

var mat = (StandardMaterial3D)Mesh.SurfaceGetMaterial(0);
mat = (StandardMaterial3D)mat.Duplicate();
mat.EmissionEnabled = true;
Mesh.SurfaceSetMaterial(0, mat);

And it still affects every instance of the scene!!

What am I doing wrong here?

Answer 1

Local to the scene only works for scenes set up in editor. When doing it in code, YOu have to use duplicate()
However, You have to notice, that there are 3 material slots in MeshInstance !. If you kept materials in the mesh property, You will have to make mesh unique/ duplicate as well!
Finally, remember that shader file, whoch is part of shader material, is also a resource. So if visual difference depends on shader code, not just shader_params - You have to make this one unique too.