constraints & tableoid [pgsql8.1]

jw=# CREATE TABLE base ( CHECK (tableoid = 'base'::regclass) );
CREATE TABLE
jw=# \d base   Table "public.base"Column | Type | Modifiers
--------+------+-----------
Check constraints:   "base_tableoid_check" CHECK (tableoid = 'base'::regclass::oid)

jw=# INSERT INTO base DEFAULT VALUES ;
ERROR:  new row for relation "base" violates check constraint
"base_tableoid_check"
jw=#