BUG #13501: Bug with subqueries in WHERE clause

The following bug has been logged on the website:

Bug reference:      13501
Logged by:          Egidio Caprino
Email address:      me@egidiocaprino.it
PostgreSQL version: 9.3.6
Operating system:   Linux (don't know the distribution)
Description:

This query returns one record

select *
from merge.organization
where school_id = 1000056

This query returns no record

select *
from merge.account
where school_id = 1000056

This query returns no record

select *
from merge.sd3_hierarchy
where school_id = 1000056

This query returns no record

select *
from merge.organization
where school_id not in (select school_id from merge.account)
or school_id not in (select school_id from merge.sd3_hierarchy)

So I have one organisation that does not exists in the account table and
does not exist in the sd3_hierarchy. The last should return at least one
record.