BUG #2549: problem with NATURAL JOIN

The following bug has been logged online:

Bug reference: 2549
Logged by: Kayteck
Email address: kayteck_master(at)o2(dot)pl
PostgreSQL version: 8.1.3
Operating system: Fedora Core 4
Description: problem with NATURAL JOIN
Details:

I have two tables joined by foreign key id_przelewu, and for some rows
results of queries with NATURAL JOIN and JOIN ... USING (...) differs ! I've
readed that NATURAL JOIN is only shorthand for the second method, but this
results shows that's not true:
select id_zamowienia,id_przelewu from zamowienia where id_klienta=4999;
id_zamowienia | id_przelewu
---------------+-------------
7504 | 3095
7503 | 3095
7408 | 3095
(3 rows)

select id_przelewu from przelew where id_przelewu=3095;
id_przelewu
-------------
3095
(1 row)

select id_przelewu,id_zamowienia from zamowienia natural join przelew where
id_klienta=4999;
id_przelewu | id_zamowienia
-------------+---------------
(0 rows)

select id_przelewu,id_zamowienia from zamowienia join przelew using (id_p
rzelewu) where id_klienta=4999;
id_przelewu | id_zamowienia
-------------+---------------
3095 | 7504
3095 | 7503
3095 | 7408
(3 rows)

It seems for an error of postgresql