BUG #6707: ERROR: could not open relation with OID

The following bug has been logged on the website:

Bug reference:      6707
Logged by:          LiFeAiR
Email address:      lifeair@gmail.com
PostgreSQL version: 9.1.4
Operating system:   FREE BSD
Description:=20=20=20=20=20=20=20=20

CREATE OR REPLACE FUNCTION test() RETURNS integer AS
$BODY$
DECLARE
 _r RECORD;
BEGIN
CREATE TEMP TABLE test(id int);
_r :=3D ROW(NULL)::test;
_r:=3DNULL;
DROP TABLE test CASCADE;
RETURN    1;
END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

  select test();