Problems with arrays

I am trying to use the array types in PgSQL, and am obviously missing
something!

swipe2test=> create table test_arr (id integer, ratecardlist integer[]);
CREATE TABLE
swipe2test=> insert into test_arr (id) values (1);
INSERT 183981491 1
swipe2test=> select * from test_arr;
id | ratecardlist
----+--------------
1 | (null)
(1 row)

swipe2test=> update test_arr set ratecardlist[1:3] = '{3,4,5}' where id = 1;
UPDATE 1

swipe2test=> select * from test_arr;
id | ratecardlist
----+--------------
1 | (null)
(1 row)

Er - huh?

So what did I miss?

Regards,
Harry.