Query not working as expected...

I don't know if this is a bug or my lack of understanding of how the query is
working. I have this table:

test=# select * from dates2;

did | date | type | timestamp | cid
------+------------+--------------+------------------------+------
5647 | 2002-05-06 | Open | 2002-05-06 13:28:35-04 | 1039
5648 | 2002-07-27 | Schedule | 2002-05-06 13:28:35-04 | 1039
5708 | 2002-05-15 | Edit | 2002-05-15 11:12:09-04 | 1039
5709 | 2002-05-15 | Edit | 2002-05-15 11:39:59-04 | 1039
5710 | 2002-05-15 | Edit | 2002-05-15 11:41:01-04 | 1039
5711 | 2002-05-15 | Edit | 2002-05-15 11:41:37-04 | 1039
5712 | 2002-05-15 | Open | 2002-05-15 14:34:32-04 | 1053
5713 | 2002-05-26 | Schedule | 2002-05-15 14:34:32-04 | 1053
5714 | 2002-05-15 | Open | 2002-05-15 14:36:00-04 | 1054
5715 | 2002-05-15 | Schedule | 2002-05-15 14:36:00-04 | 1054
5716 | 2002-05-15 | Edit | 2002-05-15 14:36:25-04 | 1054
5717 | 2002-05-15 | Edit | 2002-05-15 14:37:06-04 | 1054
5718 | 2002-05-15 | Edit | 2002-05-15 14:37:13-04 | 1054
5728 | 2002-05-15 | Approve | 2002-05-15 14:45:49-04 | 1054
5729 | 2002-05-19 | Notify | 2002-05-15 14:45:59-04 | 1054
5730 | 2002-05-21 | Complete | 2002-05-15 14:46:28-04 | 1054
5731 | 2002-05-15 | Close | 2002-05-15 14:46:28-04 | 1054
5732 | 2002-05-27 | Schedule | 2002-05-15 15:24:30-04 | 1039
5733 | 2002-05-15 | Edit | 2002-05-15 11:41:37-04 | 1055
5734 | 2002-05-15 | Edit | 2002-05-15 11:41:01-04 | 1055
5735 | 2002-05-15 | Edit | 2002-05-15 11:39:59-04 | 1055
5736 | 2002-05-15 | Edit | 2002-05-15 11:12:09-04 | 1055
5737 | 2002-05-06 | Open | 2002-05-06 13:28:35-04 | 1055
5738 | 2002-05-27 | Schedule | 2002-05-15 15:24:30-04 | 1055
5739 | 2002-07-27 | Schedule | 2002-05-06 13:28:35-04 | 1055
5740 | 2002-07-23 | Schedule | 2002-05-15 15:33:00-04 | 1055
(26 rows)

I want to extract only the most recently added rows that are uniquely defined
by cid and type.

test=# select distinct on (cid,type) * from dates2
order by cid,type,timestamp desc;

did | date | type | timestamp | cid
------+------------+--------------+------------------------+------
5711 | 2002-05-15 | Edit | 2002-05-15 11:41:37-04 | 1039
5647 | 2002-05-06 | Open | 2002-05-06 13:28:35-04 | 1039
5732 | 2002-05-27 | Schedule | 2002-05-15 15:24:30-04 | 1039
5712 | 2002-05-15 | Open | 2002-05-15 14:34:32-04 | 1053
5713 | 2002-05-26 | Schedule | 2002-05-15 14:34:32-04 | 1053
5728 | 2002-05-15 | Approve | 2002-05-15 14:45:49-04 | 1054
5731 | 2002-05-15 | Close | 2002-05-15 14:46:28-04 | 1054
5730 | 2002-05-21 | Complete | 2002-05-15 14:46:28-04 | 1054
5718 | 2002-05-15 | Edit | 2002-05-15 14:37:13-04 | 1054
5729 | 2002-05-19 | Notify | 2002-05-15 14:45:59-04 | 1054
5714 | 2002-05-15 | Open | 2002-05-15 14:36:00-04 | 1054
5715 | 2002-05-15 | Schedule | 2002-05-15 14:36:00-04 | 1054
5733 | 2002-05-15 | Edit | 2002-05-15 11:41:37-04 | 1055
5737 | 2002-05-06 | Open | 2002-05-06 13:28:35-04 | 1055
5740 | 2002-07-23 | Schedule | 2002-05-15 15:33:00-04 | 1055
(15 rows)

Now, I want only those rows from the subquery that have a date between
2002-05-17 and 2002-05-31 and a type of "Schedule".

test=# select * from (select distinct on (cid,type) * from dates2 order by
cid,type,timestamp desc) as foo
where type='Schedule' and foo.date between '2002-05-17' and '2002-05-31';

did | date | type | timestamp | cid
------+------------+--------------+------------------------+------
5732 | 2002-05-27 | Schedule | 2002-05-15 15:24:30-04 | 1039
5713 | 2002-05-26 | Schedule | 2002-05-15 14:34:32-04 | 1053
5738 | 2002-05-27 | Schedule | 2002-05-15 15:24:30-04 | 1055
(3 rows)

Notice the last row. The row with did 5738 is NOT in the result set from the
second query, which is the subquery of the above command. So why is this
showing up in the results? Anyone have an idea?
--
Titus Anderson