BUG #1295: Problem on trigger

The following bug has been logged online:

Bug reference: 1295
Logged by: shancheng

Email address: sd_shancheng(at)hotmail(dot)com

PostgreSQL version: 8.0 Beta

Operating system: Fedora2

Description: Problem on trigger

Details:

I have a table for test.
CREATE TABLE _test(id int);
Then i insert some records(at least 3 records for obvious result) into the
table:
INSERT INTO _test VALUES(1);
INSERT INTO _test VALUES(2);
INSERT INTO _test VALUES(3);

And below is my testing function and the point where the problem comes from:
CREATE OR REPLACE FUNCTION _test_delete_and_drop()
RETURNS void AS $$
BEGIN
DELETE FROM _test;
DROP TABLE _test;
RETURN;
END;
$$ LANGUAGE plpgsql;

When i run the command:
SELECT _test_delete_and_drop();
The computer responses:
ERROR: relation with OID 1354613 does not exist
CONTEXT: SQL query "DELETE FROM _test"
PL/pgSQL function "_test_delete_and_drop" line 2 at SQL statement

The function is very easy. It just delete the contents of a table and then
drop it.
The reason that i don't drop the table directly is that i need some cleanup
operations. I define several triggers on the table. And when i delete
records, the trigger will be activeted. If i don't drop the records
beforehand, there will be much useless information left in the database. But
i met a very puzzling problem when i do that. So i write the above test case
to find out what the problem is. And to simplify the question, i don't
define triggers for the table.
Could anyone help me?

Thanks very much!