drop table cascade doesn't drop manual sequences

Hello folks,

I'm new to postgres and I'm using version 8.1

Here's the problem anyway:

If I insert a sequence later on table creation with alter table, drop
table cascade simply doesn't drop this sequence even when I specify
CASCADE.

works
####################

create table bla(id serial);
drop table bla CASCADE;
select * from pg_class were relkind = 'S' => nothing

doesn't
####################

create table bla(id integer);
create sequence bla_id_seq;
alter table bla alter column id set default nextval('bla_id_seq');

drop table bla CASCADE;
select * from pg_class were relkind = 'S' => 'bla_id_seq'

Is this supposed to happen or am I missing something?

Thanks in advance,
Guilherme