Mesh not valid after setVertex

Hi,

I have strange issue with rhino mesh setVertex method

This one produces invalid mesh:

  M.Vertices.SetVertex(3, M.Vertices[0].X, M.Vertices[0].Y, M.Vertices[0].Z);

This one produces valid mesh:

    M.Vertices.SetVertex(3, M.Vertices[0].X + 0.01, M.Vertices[0].Y, M.Vertices[0].Z);

Why?

I basically would like to change vertex position to other vertex position.

I tried to use wb to unify mesh windings, after that mesh is good.

I do not know what is the magic inside unify mesh windings, but if there is some approach to clean mesh with rhinocommon would be much appreciated. Tried all these:

    M.Vertices.CombineIdentical(true, true);
    M.Vertices.CullUnused();
    M.Weld(3.14159265358979);
    M.Normals.ComputeNormals();
    M.UnifyNormals();
    M.Compact();

Mesh is still invalid.

Mesh is attached .