BUG #5123: bug in window function "last_value"

The following bug has been logged online:

Bug reference: 5123
Logged by: Andrey
Email address: andrey(at)ulab(dot)ru
PostgreSQL version: 8.4.1-x86_64
Operating system: RHEL5-x86_64
Description: bug in window function "last_value"
Details:

EXAMPLE:

CREATE TABLE t
(
id serial NOT NULL,
CONSTRAINT pkey_t PRIMARY KEY (id)
)
WITH (OIDS=FALSE);

INSERT INTO t VALUES(default);
INSERT INTO t VALUES(default);
INSERT INTO t VALUES(default);

select id, first_value(id) over(order by id), last_value(id) over(order by
id) from t;

RESULT:
id | first_value | last_value
----+-------------+------------
1 | 1 | 1
2 | 1 | 2
3 | 1 | 3
(3 rows)

fist_value - good, last_value - bad