Review changes.

lib/iris/experimental/ugrid/mesh.py

@@ -2814,16 +2814,19 @@ def axis(self):
 
     @property
     def coord_system(self):
-        """The coordinate-system of a MeshCoord comes from the related mesh coord."""
+        """The coordinate-system of a MeshCoord.
+
+        It comes from the `related` location coordinate in the mesh.
+        """
         # This matches where the coord metadata is drawn from.
         # See : https://github.com/SciTools/iris/issues/4860
         select_kwargs = {
             f"include_{self.location}s": True,
             "axis": self.axis,
         }
         try:
-            # NOTE: at present, a MeshCoord *always* references a related mesh coord of
-            # its location, from which it's points are taken.
+            # NOTE: at present, a MeshCoord *always* references the relevant location
+            # coordinate in the mesh, from which its points are taken.
             # However this might change in future ..
             # see : https://github.com/SciTools/iris/discussions/4438#bounds-no-points
             location_coord = self.mesh.coord(**select_kwargs)

lib/iris/tests/integration/experimental/test_meshcoord_coordsys.py

@@ -110,3 +110,20 @@ def test_assigned_mesh_cs(tmp_path):
     #  since there are no dim-coords, or any other coord with a c-s.
     # TODO: this may be a mistake -- see https://github.com/SciTools/iris/issues/6051
     assert cube.coord_system() is assigned_cs
+
+
+def test_meshcoord_coordsys_copy(tmp_path):
+    # Check that copying a meshcoord with a coord system works properly.
+    nc_path = tmp_path / "test_temp.nc"
+    make_file(nc_path)
+    with PARSE_UGRID_ON_LOAD.context():
+        cube = iris.load_cube(nc_path, "node_data")
+    node_coord = cube.mesh.coord(include_nodes=True, axis="x")
+    assigned_cs = GeogCS(1.0)
+    node_coord.coord_system = assigned_cs
+    mesh_coord = cube.coord(axis="x")
+    assert mesh_coord.coord_system is assigned_cs
+    meshco_copy = mesh_coord.copy()
+    assert meshco_copy == mesh_coord
+    # Note: still the same object, because it is derived from the same node_coord
+    assert meshco_copy.coord_system is assigned_cs