After upgrade from 10.2.0.4 to 11.1.0.7 behaviour changed for default value of assign of alter table

 Hi ,         Client has recently upgraded  the database from 10.2.0.4 to 11.1.0.7.After that there is a peculiar behaviour in colums data of recently created table.
SQL> SELECT SYSDATE, systimestamp FROM dual;
SYSDATE   SYSTIMESTAMP
--------- ---------------------------------------------------------------------------
01-FEB-11 01-FEB-11 10.30.47.671152 AM +08:00

Elapsed: 00:00:00.00
SQL>
SQL> CREATE TABLE test_table
  2  (
  3    test_table_oid  VARCHAR2(25) NOT NULL,
  4    ts_field        TIMESTAMP(6) DEFAULT SYSDATE NOT NULL
  5  )
  6  TABLESPACE users;

Table created.

Elapsed: 00:00:00.04
SQL>
SQL> INSERT INTO test_table (test_table_oid) VALUES ('1');

1 row created.

Elapsed: 00:00:00.00
SQL> INSERT INTO test_table (test_table_oid, ts_field) VALUES ('2', SYSDATE);

1 row created.

Elapsed: 00:00:00.00
SQL> INSERT INTO test_table (test_table_oid, ts_field) VALUES ('3', systimestamp);