BUG #3826: Very Slow Execution of examplequery (wrong plan?)

The following bug has been logged online:

Bug reference:      3826
Logged by:          Alexander Steffens
Email address:      mail@a-st.de
PostgreSQL version: 8.3b4
Operating system:   Win2003R2x64
Description:        Very Slow Execution of examplequery (wrong plan?)
Details:

Hello, I have found an Query (with data)
that need to execute on MS-SQL 2005 < 9sec,
on Postgresql I will stop it now after more than 30 mins:

create table t1 (a int);
create table t2 (a int);

insert into t1 select 1; --for t-sql compat
insert into t1 select 2;insert into t1 select 3;

insert into t2 select 1;
insert into t2 select 2;
insert into t2 select 5;

--execute 8 times QUERY A
insert into t1
select distinct (t1.a + t2.a)*2
from t1,t2
where not exists (
 select * from t1  tt where tt.a = (t1.a + t2.a)*2
)

--execute 1 times
insert into t2
select distinct (t1.a + t2.a)*3
from t1,t2
where not exists (
 select * from t2  tt where tt.a = (t1.a + t2.a)*3
)

--
--data now t1: 1642 t2: 3301
--
--now again QUERY A
--will need much too much time:
insert into t1
select distinct (t1.a + t2.a)*2
from t1,t2
where not exists (
 select * from t1  tt where tt.a = (t1.a + t2.a)*2
)

Alex.