Why does this happen ?

SQL> SELECT 1,2,3 FROM DUAL
2 GROUP BY CUBE(1,2,3);

1 2 3
---------- ---------- ----------
1 2 3

SQL> SELECT * FROM
2 (SELECT 1,2,3 FROM DUAL
3 GROUP BY CUBE(1,2,3)
4 );

1 2 3
---------- ---------- ----------
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3

8 ROWS SELECTED