delete and select with IN clause issues

I'm having problem with a cleanup script that runs nightly.  The script calls 
the following query:

delete from visit where id not in (select distinct visit_id from page_view);

This yields the following error:

ERROR:  update or delete on "visit" violates foreign key constraint 
"fk34afd255fbacabec" on "page_view"
DETAIL:  Key (id)=(38635629) is still referenced from table "page_view".

Ok, that seems fine, but when I do a select instead of delete, I do not 
find the referenced id in my list:

select id  from visit where id not in (select distinct visit_id from page_view) and id = 38635629 ;
 id
----
(0 rows)

Also, if I don't specify the id = bit at the end, I still don't find it in the 
output when I search through with less, so why is it trying to delete that 
row?

Rewriting the query like so, yields the same problem:

delete from visit where NOT EXISTS ( select * from page_view WHERE visit.id = 
page_view.visit_id);

ERROR:  update or delete on "visit" violates foreign key constraint 
"fk34afd255fbacabec" on "page_view"
DETAIL:  Key (id)=(38638264) is still referenced from table "page_view".

The plan looks like this:

explain analyze delete from visit where id not in (select distinct visit_id 
from page_view);

QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------------------
SeqScan on visit  (cost=165027.49..189106.89 rows=211976 width=6) (actual time=4789.595..5330.367 rows=150677 loops=1)
Filter: (NOT (hashed subplan))   SubPlan     ->  Unique  (cost=0.00..165017.77 rows=3889 width=8) (actual
time=2.717..4388.928rows=273285 loops=1)           ->  Index Scan using page_view_visit_idx on page_view
(cost=0.00..159625.41rows=2156946 width=8) (actual time=2.713..2914.944 rows=2249576 loops=1) Trigger for constraint
fk34afd255fbacabec:time=7174.540 calls=150677 Total runtime: 32772.345 ms
 
(7 rows)

\d page_view                      Table "public.page_view"     Column     |            Type             |
Modifiers
----------------+-----------------------------+--------------------- id             | bigint                      | not
nullvisit_id       | bigint                      | not null uri            | character varying(255)      | params
 | text                        | stamp          | timestamp without time zone | cindex         | integer
    | not null default -1 tindex         | integer                     | not null default -1 method         | character
varying(7)       | not null source_address | character varying(16)       | server_name    | character varying(255)
|
Indexes:    "page_view_pkey" PRIMARY KEY, btree (id)    "page_view_stamp_idx" btree (stamp)    "page_view_uri_idx"
btree(uri)    "page_view_visit_idx" btree (visit_id)
 
Foreign-key constraints:    "fk34afd255fbacabec" FOREIGN KEY (visit_id) REFERENCES visit(id)

What kind of silliness am I forgetting?

-- 
Jeff Frost, Owner     <jeff@frostconsultingllc.com>
Frost Consulting, LLC     http://www.frostconsultingllc.com/
Phone: 650-780-7908    FAX: 650-649-1954