SQL & PL/SQL :: Novalidate Constraint Method

NOVALIDATE CONSTRAINT METHOD.

Below is the step i gone through:

1) CREATE TABLE mutu (id NUMBER, text VARCHAR2(20));

2) INSERT INTO mutu SELECT rownum , 'mutu' FROM dual CONNECT BY LEVEL <= 10000;

3) Insert Duplicate row.
INSERT INTO mutu VALUES (42, 'DUPLICATE');

4) COMMIT;

5)Create a NON-UNIQUE INDEX's CONSTRAINT as below.
ALTER TABLE mutu ADD CONSTRAINT mutu_pk PRIMARY KEY(id)
USING INDEX(CREATE INDEX mutu_pk ON mutu(id)) ENABLE NOVALIDATE;

6) Insert Duplicate row.
INSERT INTO mutu VALUES (42, 'DUPLICATE');

7) ERROR at line 1:
ORA-00001: unique constraint (SYS.ZIGGY_PK) violated

Why it shows the error. Even though I had created a NON-UNIQUE INDEX's Constraint only.