BUG #5681: Using set returning function as subrequest can result losing rows in result set

The following bug has been logged online:

Bug reference:      5681
Logged by:          Maksym Boguk
Email address:      Maxim.Boguk@gmail.com
PostgreSQL version: 8.4.4
Operating system:   FreeBSD 7.2
Description:        Using set returning function as subrequest can result
losing rows in result set
Details:

There is simplified version of real query:

CREATE OR REPLACE FUNCTION test_entity(integer) RETURNS SETOF integer
LANGUAGE sql STABLE ROWS 1
AS $_$
    SELECT id FROM entities WHERE id=$1;
$_$;

Full result query:

SELECT
   r.id
   ,s.id
   ,s.entity_id
--   ,test_entity(s.entity_id)
   FROM resstat_2010_09 r
   JOIN services s ON s.id = r.service_id
WHERE r.lbill_id=1200;

    id     |   id    | entity_id
-----------+---------+-----------
 141798910 | 7004573 |    242023
 141798911 | 7004578 |    242023
 141798912 | 7004577 |    242023
 141798913 | 7004579 |    242023
 141798964 | 7004583 |    242023
 141799001 | 7004584 |
 141802715 | 7004707 |
(7 rows)

Now lets uncomment set returning function:
SELECT
   r.id
   ,s.id
   ,s.entity_id
   ,test_entity(s.entity_id)
   FROM resstat_2010_09 r
   JOIN services s ON s.id = r.service_id
WHERE r.lbill_id=1200 ORDER BY r.id;

    id     |   id    | entity_id | test_entity
-----------+---------+-----------+-------------
 141798910 | 7004573 |    242023 |      242023
 141798911 | 7004578 |    242023 |      242023
 141798912 | 7004577 |    242023 |      242023
 141798913 | 7004579 |    242023 |      242023
 141798964 | 7004583 |    242023 |      242023
(5 rows)

Oops... two rows where function returned zero rows just disappeared.

Explain analyze of the both cases looks completely same:

billing_test=# EXPLAIN ANALYZE SELECT
   r.id
   ,s.id
   ,s.entity_id
   ,test_entity(s.entity_id)
   FROM resstat_2010_09 r
   JOIN services s ON s.id = r.service_id
WHERE r.lbill_id=1200 ORDER BY r.id;

QUERY PLAN
----------------------------------------------------------------------------
----------------------------------------------------------------------------
-----
 Sort  (cost=9.38..9.41 rows=10 width=12) (actual time=0.872..0.897 rows=5
loops=1)
   Sort Key: r.id
   Sort Method:  quicksort  Memory: 25kB
   ->  Nested Loop  (cost=0.00..9.22 rows=10 width=12) (actual
time=0.307..0.810 rows=5 loops=1)
         ->  Index Scan using resstat_2010_09_lbill_id_key on
resstat_2010_09 r  (cost=0.00..1.62 rows=10 width=8) (actual
time=0.036..0.084 rows=7 loops=1)
               Index Cond: (lbill_id = 1200)
         ->  Index Scan using services_pkey on services s  (cost=0.00..0.50
rows=1 width=8) (actual time=0.015..0.021 rows=1 loops=7)
               Index Cond: (s.id = r.service_id)
 Total runtime: 1.045 ms
(9 rows)

PS: I know using set return function in that way is bad style. But I think
behavior is wrong.

PPS: any chance make evaluating of subrequest function visible in explain
output in the future?

Thanks for youre attention.