Foreign key constraint referencing a parent table

Hi,

I have a problem when inserting rows into my table tblfactuurpost that
references a table tblfactuur which is a parent to tblclientfactuur.
The actual row is inserted into tblfactuur.

The problem is that i cannot insert the row into tblfactuurpost (which
references the parent table tblfactuur) because PSQL complains the
referencing ID (2) is missing while it is actually *not* missing at all.

Thanks to anyone who can shed some light ...

I have the following table set-up:

CREATE TABLE tblfactuur (id serial PRIMARY KEY,number int NOT NULL,year int NOT NULL CHECK (year>=1900 AND year<=2999),
vanaf date NOT NULL,tot date NOT NULL CHECK (tot > vanaf),
total int -- totaalbedrag in centen
);

CREATE TABLE tblclientfactuur (client int NOT NULL REFERENCES tblclient (id) ON DELETE RESTRICT, PRIMARY KEY (id)
) INHERITS (tblfactuur);

CREATE TABLE tblfactuurpost (id serial PRIMARY KEY,factuur int NOT NULL REFERENCES tblfactuur (id) ON DELETE CASCADE
DEFERRABLE,
omschrijving varchar(128),
btw smallint DEFAULT 19, -- standaard 19% btwaantal decimal(8,1) NOT NULL CHECK (aantal >= 0), -- aantalperstuk int NOT
NULLCHECK (perstuk >= 0), -- bedrag per stuk in  
centenamount int NOT NULL CHECK (amount >= 0), -- totaal bedrag in centen
position smallint CHECK (position >= 0)
);

This is the data in tblfactuur:

(db)=> select * from tblfactuur;id | number | year |   vanaf    |    tot     | total
----+--------+------+------------+------------+-------- 2 |      1 | 2010 | 2010-03-01 | 2010-04-01 | 397800
(1 row)

I try to insert:

insert into tblfactuurpost (factuur, omschrijving, btw, aantal, perstuk,

amount, position)select ?, ?, ?, ?, ?, ?, count(*) from tblfactuurpost where factuur

= ?;
parameters: (2, Gespecialiseerde 24 uur zorg ma. t/m vr., 19, 156, 1425,

397800, 2)

Regards, David