Bug #731: Same SQL produces different results before and after VACUUM FULL

Henry (henry(at)ssc-ltd(dot)com) reports a bug with a severity of 1
The lower the number the more severe it is.

Short Description
Same SQL produces different results before and after VACUUM FULL

Long Description
We have run the SQL statement below before and after VACUUM FULL.
Before VACUUM FULL, it returns 3615 records.
After VACUUM FULL, it return 34123 records which is the result I expect.
Before VACUUM FULL, if I change the LEFT OUTER JOIN to join the table a, it returns 34123 records.

I have a daily backup job which executes VACUUM ANALYSE daily.

I don't know what causes the problem. Please help!!!!

Sample Code

SELECT *
from (SELECT pbdedup_party_1.party_id
from pbdedup_party_1
where pbdedup_party_1.batch_no = ?
UNION
SELECT pbdedup_party_2.party_id
from pbdedup_party_2
where pbdedup_party_2.batch_no = ?
) as a
, pb_person
left outer join pbdedup_person_parts ON pb_person.party_id = pbdedup_person_parts.party_id
where a.party_id = pb_person.party_id

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