Bug on PostgreSQL 9.4.4

test_perform_bug_on_unique_column.sql

DROP TABLE test;
SELECT * FROM test;

CREATE TABLE test (
  id SERIAL,
  name TEXT
);

INSERT INTO test (name) VALUES ('a'), ('b'), ('c'), ('d'), ('e'), ('f'), ('g'), ('h');

CREATE OR REPLACE FUNCTION test_perform_bug_on_unique_column()
  RETURNS TEXT AS $$
DECLARE
    d_code TEXT;
    d_count INT;
BEGIN

d_count := 0;
LOOP

	SELECT string_agg(SUBSTRING(cs.chars FROM ceil((char_length(cs.chars) * random())) :: INT FOR 1), '')
	FROM generate_series(1, 1, 1) CROSS JOIN (SELECT 'abcdefgh' :: TEXT AS chars) AS cs INTO d_code;

        PERFORM TRUE FROM test WHERE code=d_code;
            IF (NOT FOUND) THEN
		RETURN d_code;
            END IF;
    d_count := d_count + 1;
    EXIT WHEN d_count > 500;
END LOOP;

        RAISE EXCEPTION 'Failed to generate Account code';

END;
$$ LANGUAGE plpgsql;

ALTER TABLE test ADD COLUMN code TEXT DEFAULT test_perform_bug_on_unique_column() UNIQUE;