以 2 而不是 1 开头的 Oracle 序列

I am encountering strange behavior of Oracle sequences with 11g (works with 10g):

CREATE SEQUENCE test_sequence START WITH 1;
CREATE TABLE test_table ( val INT );

INSERT INTO test_table VALUES ( test_sequence.NEXTVAL );

即使序列以1开头，插入的第一个值是2:

SELECT * FROM test_table;

       VAL
----------
         2

CREATE SEQUENCE test_sequence_2 START WITH 1;

SELECT test_sequence_2.NEXTVAL FROM dual

   NEXTVAL
----------
         1