select version();
 PostgreSQL 8.4.6 on i386-apple-darwin, compiled by GCC i686-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5370), 32-bit
 PostgreSQL 9.1.1 on x86_64-apple-darwin10.8.0, compiled by i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5666) (dot 3), 64-bit


drop table if exists t2;


create table t2 (

    a text not null,
    b text null,

    constraint t2_pk primary key (a),

    constraint t2_t2_fk foreign key (b)
       references t2 (a) match simple
           on update cascade            --  !
           on delete cascade
               deferrable
               initially deferred       --  !
);

--Test data
insert into t2
values
    ('asd', 'www'),
    ('www', 'asd');

start transaction;
    set constraints all immediate;  -- If not switched then everything is ok
--    set constraints all deferred;

    update t2
    set a = '123'
    where a = 'asd';

    select * from t2;

    update t2
    set a = 'kkk'
    where a = '123'; --have a error here

commit;