to_timestamp busted?

I have gotten some interesting results in testing out date
conversions using to_timestamp.

Given the query:

[NB: log_date and log_time are both varchar fields.
Yes I am yet another person parsing web server logs....]

SELECT timestamp(log_date || ' ' || log_time),
log_date,
log_time
FROM iis_log limit 10 ;

I get:
timestamp | log_date | log_time
------------------------+------------+----------
2001-06-20 00:05:54-04 | 2001-06-20 | 00:05:54
2001-06-23 00:01:45-04 | 2001-06-23 | 00:01:45
2001-06-20 23:58:45-04 | 2001-06-20 | 23:58:45
2001-06-23 00:01:48-04 | 2001-06-23 | 00:01:48
2001-06-20 23:59:03-04 | 2001-06-20 | 23:59:03
2001-06-23 00:02:42-04 | 2001-06-23 | 00:02:42
2001-06-20 00:05:46-04 | 2001-06-20 | 00:05:46
2001-06-23 00:02:48-04 | 2001-06-23 | 00:02:48
2001-06-20 23:59:03-04 | 2001-06-20 | 23:59:03
2001-06-23 00:03:15-04 | 2001-06-23 | 00:03:15
(10 rows)

which looks good to me.

But using:

SELECT to_timestamp(log_date || ' ' || log_time,
'YYYY-MM-DD HH24:MM:SS'),
log_date,
log_time
FROM iis_log limit 10;

I get the bizarre results of:

to_timestamp | log_date | log_time
------------------------+------------+----------
2001-05-20 00:00:54-04 | 2001-06-20 | 00:05:54
2001-01-23 00:00:45-05 | 2001-06-23 | 00:01:45
2005-10-20 23:00:45-04 | 2001-06-20 | 23:58:45
2001-01-23 00:00:48-05 | 2001-06-23 | 00:01:48
2005-11-20 23:00:03-05 | 2001-06-20 | 23:59:03
2001-02-23 00:00:42-05 | 2001-06-23 | 00:02:42
2001-05-20 00:00:46-04 | 2001-06-20 | 00:05:46
2001-02-23 00:00:48-05 | 2001-06-23 | 00:02:48
2005-11-20 23:00:03-05 | 2001-06-20 | 23:59:03
2001-03-23 00:00:15-05 | 2001-06-23 | 00:03:15
(10 rows)

Anyone seen this before?

thanks,
eliel