Weirdess when altering serial column type

Should that sequence really stick around as an integer, numeric and text
field???

test=# create table test (a serial);
NOTICE: CREATE TABLE will create implicit sequence "test_a_seq" for
serial column "test.a"
NOTICE: CREATE TABLE will create implicit sequence "test_a_seq" for
serial column "test.a"
CREATE TABLE
test=# \d test
Table "public.test"
Column | Type | Modifiers
--------+---------+-----------------------------------------------------
a | integer | not null default nextval('public.test_a_seq'::text)

test=# alter table test alter a type integer;
ALTER TABLE
test=# \d test
Table "public.test"
Column | Type | Modifiers
--------+---------+-----------------------------------------------------
a | integer | not null default nextval('public.test_a_seq'::text)

test=# alter table test alter a type numeric;
ALTER TABLE
test=# \d test
Table "public.test"
Column | Type | Modifiers
--------+---------+-----------------------------------------------------
a | numeric | not null default nextval('public.test_a_seq'::text)

test=# alter table test alter a type text;
ALTER TABLE
test=# \d test
Table "public.test"
Column | Type | Modifiers
--------+------+-----------------------------------------------------
a | text | not null default nextval('public.test_a_seq'::text)