Missing value from PostgreSQL query?

Hi all,
Does any one know why I have following inconsistant results from
PostgreSQL under Cygwin?

When I switch the select order, or use "select * from patient", some
values are missing from returned results.

What might be wrong?

Thanks in advance.

test=# select first_name, last_name, used, birthday from patient;
first_name | last_name | used | birthday
------------+-----------+------+------------
| 1960-02-01DI | N
| 1960-02-01DI | N
(2 rows)

test=# select first_name, last_name, birthday, used from patient;
first_name | last_name | birthday | used
------------+-----------+------------+------
AAAAAA | TDI | 1960-02-01 | N
AAAAAB | TDI | 1960-02-01 | N
(2 rows)
/* worked fine */

est=# select birthday from patient;
birthday
------------
1960-02-01
1960-02-01
(2 rows)

test=# select used from patient;
used
------
N
N
(2 rows)

test=# select used, birthday from patient;
used | birthday
------+------------
| 1960-02-01
| 1960-02-01
(2 rows)

Jason