drop a constraint

Hello,
I create my constraint like this :

drop table table1;
drop table table2;
CREATE table table1 (id int4, id_dest int4);
CREATE table table2 (id int4,id_dest int4);
ALTER TABLE table1 add constraint table1_id_table2_id_dest foreign key(id_dest) references table2(id);

drop view dev_ri;
CREATE VIEW dev_ri
AS
SELECT t.oid as trigoid
,c.relname as trig_tbl
,t.tgname
,t.tgfoid
-- ,f.proname as trigfunc
-- ,t.tgenabled
-- ,t.tgconstrname
,c2.relname as const_tbl
-- ,t.tgdeferrable
-- ,t.tginitdeferred
,t.tgargs
FROM pg_trigger t,
pg_class c,
pg_class c2,
pg_proc f
WHERE t.tgrelid=c.oid
AND t.tgconstrrelid=c2.oid
AND tgfoid=f.oid
AND tgname ~ '^RI_';

i list the trigger so generated :

select * from dev_ri;
trigoid | trig_tbl | tgname | tgfoid | const_tbl | tgargs
---------+----------+------------------------------+--------+-----------+----------------------------------------------------------------------------------
1641628 | table1 | RI_ConstraintTrigger_1641627 | 1644 | table2 | table1_id_table2_id_dest\000table1\000table2\000UNSPECIFIED\000id_dest\000id\000
1641630 | table2 | RI_ConstraintTrigger_1641629 | 1654 | table1 | table1_id_table2_id_dest\000table1\000table2\000UNSPECIFIED\000id_dest\000id\000
1641632 | table2 | RI_ConstraintTrigger_1641631 | 1655 | table1 | table1_id_table2_id_dest\000table1\000table2\000UNSPECIFIED\000id_dest\000id\000

And i try to drop any of this trigger generated :
=# drop trigger RI_ConstraintTrigger_1641627 on table1;
DropTrigger: there is no trigger ri_constrainttrigger_1641627 on relationtable1;

any suggestion?
do i badly name my trigger ?

thanks,