BUG #1367: Unique constraint fails with some values

The following bug has been logged online:

Bug reference: 1367
Logged by: Hong Yuan
Email address: hongyuan(at)homemaster(dot)cn
PostgreSQL version: 8.0
Operating system: Windows XP Chinese Simplified
Description: Unique constraint fails with some values
Details:

I found that the unique constraint fails sometimes when the varchar column
contain some specific Chinese characters. Here is an example:

CREATE TABLE test
(
col1 varchar(10),
CONSTRAINT col1 UNIQUE (col1)
)
WITHOUT OIDS;

insert into test values('');
insert into test values('');
insert into test values('');

While the second and third inserts should fail, they do not. With some other
Chinese characters, the constraint is observed.

The character '' has utf-8 encoding '\xe5\xa4\xa7'.

The database is created with UNICODE encoding. The problem is present with
version 8.0.0-rc2.