ERROR: replace_vars_with_subplan_refs (!?)

How should I interpret that error?

auction=# SELECT (select max(b.price) from bid b where b.auction_id = a.id and b.person_id = buyer.id) as
last_lot,auction_status(a.id)> 0 AS current, a.lot, a.person_id, next_price(a.id), seller.mail AS seller_mail,
buyer.mailAS buyer_mail, seller.locale AS seller_locale, buyer.login AS buyer_login, num_bid(a.id), seller.login AS
seller_login,t.name AS auction_type FROM auction* a, person seller, person buyer, auction_type t WHERE a.id = 84 AND
seller.id= a.person_id AND COALESCE(a.type,1) = t.id AND buyer.id = 2;
 
ERROR:  replace_vars_with_subplan_refs: variable not in subplan target list

Thanks,

-- 
Louis-David Mitterrand - ldm@apartia.org - http://www.apartia.org
Marijuana is nature's way of saying, "Hi!".