BUG #4748: hash join and sort-merge join make different results

The following bug has been logged online:

Bug reference:      4748
Logged by:          Roman Kononov
Email address:      kononov@ftml.net
PostgreSQL version: 8.3.7
Operating system:   GNU/Linux x86_64
Description:        hash join and sort-merge join make different results
Details:

test-std=# create table t(s int,i interval);
CREATE TABLE
test-std=# insert into t values (0,'30 days'), (1,'1 month');
INSERT 0 2
test-std=# select * from t as a, t as b where a.i=b.i;
 s |    i    | s |    i
---+---------+---+---------
 0 | 30 days | 0 | 30 days
 0 | 30 days | 1 | 1 mon
 1 | 1 mon   | 0 | 30 days
 1 | 1 mon   | 1 | 1 mon
(4 rows)

test-std=# analyze;
ANALYZE
test-std=# select * from t as a, t as b where a.i=b.i;
 s |    i    | s |    i
---+---------+---+---------
 0 | 30 days | 0 | 30 days
 1 | 1 mon   | 1 | 1 mon
(2 rows)