BUG #4023: The transaction control does not work for sequences

The following bug has been logged online:

Bug reference:      4023
Logged by:          Giovani Murilo Dantas Correa
Email address:      contato@isolution.inf.br
PostgreSQL version: 8.3.0 and 8.1.9
Operating system:   Linux 2.6.X (Slackware and Fedora)
Description:        The transaction control does not work for sequences
Details:

create sequence seq_test;
select nextval('seq_test'); --return value 1
select nextval('seq_test'); --return value 2
select nextval('seq_test'); --return value 3
BEGIN;
select nextval('seq_test'); --return value 4
select nextval('seq_test'); --return value 5
select nextval('seq_test'); --return value 6
ROLLBACK;
select currval('seq_test'); --return value 6

This is not right. The currval must have be 3 and not 6.