BUG #9006: Incorrect update when using where with non-existent column in subselect

The following bug has been logged on the website:

Bug reference: 9006
Logged by: Martin Nzioki
Email address: martin(dot)nzioki(at)gmail(dot)com
PostgreSQL version: 9.3.2
Operating system: Windows 7 64-bit Professional SP1
Description:

drop table if exists _test1;
drop table if exists _tmp_test2;

create table _test1 (id int not null primary key, c2 int);
insert into _test1 (id) select * from generate_series(1, 5);

create table _tmp_test2 (id_fk int not null);
insert into _tmp_test2 (id_fk) select id from _test1 limit 2;

update _test1 set c2 = 7 where id in (select id from _tmp_test2);
select * from _test1 order by id;

Expected results:
id,c2
--,--
1,7
2,7
3,
4,
5,

Actual results:
id,c2
--,--
1,7
2,7
3,7
4,7
5,7

Changing the update to

update _test1 set c2 = 7 where id in (select id_fk from _tmp_test2);

returns the expected results.

Expectation is that the non-existent id_fk would have been caught during
parsing.

This still happens even when each statement is executed in its own
transaction.

Using pgScript on pgAdmin:

[QUERY ] drop table if exists _test1
NOTICE: table "_test1" does not exist, skipping
[QUERY ] drop table if exists _tmp_test2
NOTICE: table "_tmp_test2" does not exist, skipping
[QUERY ] create table _test1 (id int not null primary key, c2 int)
[QUERY ] insert into _test1 (id) select * from generate_series(1, 5)
[QUERY ] create table _tmp_test2 (id_fk int not null)
[QUERY ] insert into _tmp_test2 (id_fk) select id from _test1 limit 2
[QUERY ] update _test1 set c2 = 7 where id in (select id from
_tmp_test2)
[QUERY ] select * from _test1 order by id