resetting serials and sequences

Hi,

#create temp table a (
id serial primary key,
name text not null);

#insert into a (name) values ('Tom');
#insert into a (name) values ('Fer');
#insert into a (name) values ('Mario');

#select * from a;
id | name
----+-------
1 | Tom
2 | Fer
3 | Mario
(3 rows)

OK. Now for some reason I need to reset everything without drop tables:

#delete from a;
#select setval ('a_id_seq', 1);
vacuum;

And now reinsert items:
#insert into a (name) values ('Tom');
#insert into a (name) values ('Fer');
#insert into a (name) values ('Mario');

#select * from a;
id | name
----+-------
2 | Tom
3 | Fer
4 | Mario
(3 rows)

We have missed the id "1"!!!

Otherway:
#select setval('a_id_seq', 0);
ERROR: a_id_seq.setval: value 0 is of of bounds (1,2147483647)

Is this a bug?

Best wishes for the brand new year \fer