Creating Face Group

function CreateFaceGroup(mesh, group_name, facet_array)
{
    mesh.beginEdit();
    if (!mesh.createFaceGroup(group_name)) 
    {
        print("Failed to create face group: " + group_name);
        return;
    }
    var face_group = mesh.getFaceGroup(mesh.getNumFaceGroups() - 1);
    for (var i = 0; i < facet_array.length; i++)
    {
        face_group.addIndex(facet_array[i]);
    }
    mesh.activateFaceGroup(mesh.getNumFaceGroups() - 1);
    mesh.finishEdit();
}

Face groups created, but vertex/face counts are zero