casting in ORDER BY

I try to fix foreign_data regression test for Czech locale (HEAD). For
example I replaced

SELECT * FROM information_schema.user_mapping_options ORDER BY 1, 2, 3,
4;

with following statement:

SELECT * FROM information_schema.user_mapping_options ORDER BY 1, 2,
3::name, 4;

which should use C sorting rules on thirds column, but it look likes
that third column is ignored. See diff:

  (4 rows)

  SET ROLE regress_test_role;
! SELECT * FROM information_schema.user_mapping_options ORDER BY 1, 2, 3, 4;
   authorization_identifier | foreign_server_catalog | foreign_server_name | option_name | option_value
  --------------------------+------------------------+---------------------+-------------+--------------
   PUBLIC                   | regression             | st1                 | modified    | 1
   regress_test_role        | regression             | s5                  | modified    | 1
-  regress_test_role        | regression             | s6                  | username    | test
   regress_test_role        | regression             | st1                 | password    | boo
   regress_test_role        | regression             | st1                 | username    | bob
  (5 rows)

--- 711,723 ----
  (4 rows)

  SET ROLE regress_test_role;
! SELECT * FROM information_schema.user_mapping_options ORDER BY 1, 2, 3::name, 4;
   authorization_identifier | foreign_server_catalog | foreign_server_name | option_name | option_value
  --------------------------+------------------------+---------------------+-------------+--------------
   PUBLIC                   | regression             | st1                 | modified    | 1
   regress_test_role        | regression             | s5                  | modified    | 1
   regress_test_role        | regression             | st1                 | password    | boo
+  regress_test_role        | regression             | s6                  | username    | test
   regress_test_role        | regression             | st1                 | username    | bob
  (5 rows)


Is it bug or I overlook something?

    Zdenek

PS: Regression test patch is attached.