help on to_date conversion please....

I am converting an 8 digit number to a date.  I don't see a postgres
function to do it direct, but two functions seems like I'm on the right
track, to_char and to_date.  Individually I get them to work, but when I
combine them I get the wrong answer.  see below.  Can anyone help in
getting the right date from an 8 digit number input formatted as yyyymmdd?


hwds=# select to_char(20020101, '99999999');
   to_char
-----------
   20020101    CORRECT.
(1 row)

hwds=# select to_date('20020101','yyyymmdd');
   to_date
------------
  2002-01-01    CORRECT.
(1 row)

hwds=# select to_date(to_char(20020101, '99999999'),'yyyymmdd');
   to_date
------------
  2003-08-12     WHY DOES IT GIVE ME DIFFERENT ANSWER WHEN I COMBINE THE
FUNCTIONS?
(1 row)