BUG #4382: there is an exagerate increase of execution times putting a 'case' condition in this update

The following bug has been logged online:

Bug reference:      4382
Logged by:          Gianluca Buttarelli
Email address:      gianluca.buttarelli@business-partner.it
PostgreSQL version: 8.1.11
Operating system:   linux
Description:        there is an exagerate increase of execution times
putting  a 'case' condition in this update
Details:

update accounts_changing set closed_sc_nowcurrent_nbr = (select count (*)
from crm_shopping_carts  ,qab_wf_states
               where  accounts_changing.account_id=crm_shopping_carts.agency_id
and  qab_wf_states.state_code in ('SC-FAT1','SC-FAT2') and
crm_shopping_carts.state_id = qab_wf_states.state_id and
               (case when ( CURRENT_DATE >  date(EXTRACT(YEAR FROM
CURRENT_DATE)||'-10-31')  and CURRENT_DATE < date(EXTRACT(YEAR FROM
CURRENT_DATE)||'-12-31'))
                then   (crm_shopping_carts.creation_date between date((EXTRACT(YEAR FROM
CURRENT_DATE))||'-11-01')  and CURRENT_DATE)
                else  (crm_shopping_carts.creation_date between date((EXTRACT(YEAR FROM
CURRENT_DATE)-1)||'-11-01')and CURRENT_DATE) end ))
                where active_indcr='1'