Ordering by field using lower()

Hi, please view the output from some queries below. My question is, why is
the ordering apparently wrong when using the lower() function?

The field "pid" is of type int2 and there is no need to use lower(), but I
will need to put a test clause in php if my order type is pid so I do not
use lower() in the query. Which is not a problem but I am interested as to
why lower() returns a different set of results when being used on int2.

Thanks.

logs=# select max(pid) from syslogd; max
-------31924
(1 row)

logs=# select min(pid) from syslogd;min
-----548
(1 row)

logs=# select pid from syslogd order by pid asc limit 10;pid
------ 548 548 548 548 548 876 876398339833983
(10 rows)

logs=# select pid from syslogd order by lower(pid) asc limit 10; pid
-------25272253892617026323299583029430294305043050431770
(10 rows)

logs=# select pid from syslogd order by pid desc limit 10; pid
-------31924319243192431924319243192331923319233192331922
(10 rows)

logs=# select pid from syslogd order by lower(pid) desc limit 10;pid
------90889088 876 876 548 548 548 548 5485158
(10 rows)

logs=#