SQL ownership and trigger insert problem

test.sql

DROP TABLE IF EXISTS parent CASCADE;
DROP TABLE IF EXISTS child;
DROP TABLE IF EXISTS log;
DROP ROLE IF EXISTS tbl_owners;

CREATE ROLE tbl_owners;
GRANT tbl_owners TO current_user;

CREATE TABLE parent (
    id SERIAL PRIMARY KEY
);

ALTER TABLE parent OWNER TO tbl_owners;

CREATE TABLE child (
    id SERIAL PRIMARY KEY,
    parent_id INTEGER,
    CONSTRAINT fk_parent FOREIGN KEY (parent_id) 
        REFERENCES parent(id) ON UPDATE CASCADE ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED
);

ALTER TABLE child OWNER TO tbl_owners; --THIS CAUSES TROUBLE

CREATE TABLE log (
	id SERIAL PRIMARY KEY,
	message TEXT
);

CREATE OR REPLACE FUNCTION add_log() RETURNS TRIGGER LANGUAGE plpgsql AS
$$
BEGIN
  INSERT INTO log (message) VALUES (TG_RELNAME || ' logged');
  RETURN NULL;
END;
$$;

CREATE TRIGGER log_parent
 BEFORE DELETE
   ON parent
EXECUTE PROCEDURE add_log();

CREATE TRIGGER log_child
	BEFORE DELETE
	ON child
EXECUTE PROCEDURE add_log();


INSERT INTO parent (id) VALUES (1);
INSERT INTO child (parent_id) VALUES (1);

DELETE FROM parent; --BOOM!

SELECT * FROM log;