BUG #5891: Unique index is not unique

The following bug has been logged online:

Bug reference: 5891
Logged by: Alexander V. Chernikov
Email address: melifaro(at)ipfw(dot)ru
PostgreSQL version: 8.4.5
Operating system: FreeBSD 7.3
Description: Unique index is not unique
Details:

Just in case if formatting is lost, this data is available at
http://postgresql.pastebin.com/4ZZdXEHB

Problem table:

meganet=# \d billing.bc_payments

Table
"billing.bc_payments"
Column | Type |
Modifiers
---------------------------+-----------------------------+------------------
-----------------------------------------------------------
bc_payment_id | integer | not null default
nextval('billing.bc_payments_bc_payment_id_seq'::regclass)
contractor_name | character varying(255) | not null

payment_date | date | not null

payment_commission_number | character varying(255) | not null

payment_sum | numeric(10,4) | not null

contractor_account | character(18) |

contractor_bik | character(8) |

inn | character varying(16) |

payment_comment | character varying(1024) |

is_assigned | bit(1) | not null default
B'0'::"bit"
assign_comment | character varying(255) |

assign_maker | integer |

assign_date | timestamp without time zone |

file_name | character varying(32) | not null

line_number | integer | not null

parse_date | timestamp without time zone | not null default
now()
Indexes:

"bc_payments_pkey" PRIMARY KEY, btree (bc_payment_id)

"bc_payments_payement_idx" UNIQUE, btree (contractor_name, payment_date,
payment_commission_number, payment_sum, contractor_account, contractor_bik,
inn)
Referenced by:


TABLE "billing.comein_accounts" CONSTRAINT
"comein_accounts_bc_payment_id_fkey" FOREIGN KEY (bc_payment_id) REFERENCES
billing.bc_payments(bc_payment_id)
TABLE "billing.payments" CONSTRAINT "payments_bc_payment_id_fkey"
FOREIGN KEY (bc_payment_id) REFERENCES billing.bc_payments(bc_payment_id)

Triggers:


londiste_replika_logger AFTER INSERT OR DELETE OR UPDATE ON
billing.bc_payments FOR EACH ROW EXECUTE PROCEDURE
pgq.logtriga('londiste.replika', 'kvvvvvvvvvvvvvvv', 'billing.bc_payments')

Problem index: bc_payments_payement_idx

Identical records:
meganet=# SELECT count(*), array_agg(bc_payment_id) FROM billing.bc_payments
GROUP BY contractor_name, payment_date, payment_commission_number,
payment_sum, contractor_account, contractor_bik, inn HAVING count(*) > 1;
count | array_agg


-------+-------------


2 | {6376,6380}


2 | {6947,6605}


(2 rows)

Data for those records (some fields data changed)
meganet=# select * from billing.bc_payments where bc_payment_id in
(6376,6380,6947,6605) order by payment_date;
bc_payment_id | contractor_name | payment_date |
payment_commission_number | payment_sum | contractor_account |
contractor_bik | inn |
payment_comment | is_assigned |
assign_comment | assign_maker | assign_date | file_name
| line_number | parse_date

---------------+------------------------+--------------+--------------------
-------+-------------+--------------------+----------------+------------+---
----------------------------------------------------------------------------
--------------------------+-------------+----------------+--------------+---
-------------------------+-----------------------+-------------+------------
----------------

6376 | ООО "XXX " | 2010-11-09 | 153
| 3416.2000 | 7028106000000XXXX8 | 44XXXXX6 | 77086XXXX6 |
Доплата за услуги связи по Договору
№2000ZZZ-2000ZZZ/0309 за ноябрь 2010г., включая |НДС 18
% - 521-12. | 1 | ok | 33 | 2010-11-09
20:08:31.28546 | sb20101109_200651.txt | 424 | 2010-11-09
20:08:31.280599

6380 | ООО "XXX " | 2010-11-09 | 153
| 3416.2000 | 7028106000000XXXX8 | 44XXXXX6 | 77086XXXX6 |
Доплата за услуги связи по Договору
№2000ZZZ-2000ZZZ/0309 за ноябрь 2010г., включая |НДС 18
% - 521-12. | 1 | ok | 33 | 2010-11-09
20:38:29.387315 | sb20101109_203358.txt | 424 | 2010-11-09
20:38:29.377831

6947 | ОАО "YYY " | 2010-12-03 | 1026
| -2200.0000 | 422810268803163353 | 445YYYY6 | 78120YYYY0 |
Оплата по счету N SCSN-67YYYY8 от 22/11/2010 г. В
т.ч.|НДС 335,59 руб.| | 1
| ok | 33 | 2010-12-09 17:22:28.891094 |
sb20101209_163201.txt | 108 | 2010-12-09 17:22:28.881133

6605 | ОАО "YYY " | 2010-12-03 | 1026
| -2200.0000 | 422810268803163353 | 445YYYY6 | 78120YYYY0 |
Оплата по счету N SCSN-67YYYY8 от 22/11/2010 г. В
т.ч.|НДС 335,59 руб.| | 1
| ok | 33 | 2010-12-09 16:10:00.176578 |
sb20101209_160846.txt | 108 | 2010-12-09 16:10:00.173055

(4 rows)

meganet=# select version();
version

----------------------------------------------------------------------------
------------------------------
PostgreSQL 8.4.5 on amd64-portbld-freebsd7.3, compiled by GCC cc (GCC)
4.2.1 20070719 [FreeBSD], 64-bit

Backup for ~pgsql/data directory with whose records exists so I can do some
additional debugging if needed