Different Pstart/Pstop same plan_hash_value

[oracle@stormking cdb12102 sqlplan]$ sqlplus /nolog @ addpartition.SQL

SQL*Plus: RELEASE 12.1.0.2.0 Production ON Sun Apr 26 13:53:06 2015

Copyright (c) 1982, 2014, Oracle.  ALL rights reserved.

Connected.
SQL> SET linesize 200
SQL> SET pagesize 0
SQL> SET trimspool ON
SQL> WHENEVER oserror EXIT 1
SQL> variable sqlid1 VARCHAR2(13)
SQL> variable cld1 NUMBER
SQL> variable phv1 NUMBER
SQL> variable sqlid2 VARCHAR2(13)
SQL> variable cld2 NUMBER
SQL> variable phv2 NUMBER
SQL> variable xplanopts VARCHAR2(40)
SQL> EXEC :xplanopts := 'basic'

PL/SQL PROCEDURE successfully completed.

SQL> EXEC :xplanopts := NULL

PL/SQL PROCEDURE successfully completed.

SQL>
SQL> DROP TABLE p;
DROP TABLE p
           *
ERROR AT line 1:
ORA-00942: TABLE OR VIEW does NOT exist


SQL>
SQL> CREATE TABLE p
  2  (
  3  pdt        DATE,
  4  a       NUMBER
  5  )
  6  PARTITION BY RANGE ( pdt )
  7  (
  8  PARTITION p20150425 VALUES less than ( TO_DATE ( '20150426', 'yyyymmdd' ) )
  9  )
 10  ;

TABLE created.

SQL>
SQL> INSERT INTO p ( pdt, a ) VALUES ( TO_DATE ( '20150425', 'yyyymmdd' ), 20150425 );

1 ROW created.

SQL>
SQL> COMMIT;

COMMIT complete.

SQL> EXEC dbms_stats.gather_table_stats(NULL,'p' );

PL/SQL PROCEDURE successfully completed.

SQL>
SQL> SELECT pdt, a FROM p WHERE pdt = TO_DATE ( '20150425', 'yyyymmdd' );
20150425 00:00   20150425

SQL> @ phv1
SQL> BEGIN
  2  SELECT sql_id, child_number, plan_hash_value INTO :sqlid1, :cld1, :phv1
  3  FROM v$sql
  4  WHERE ( sql_id, child_number ) IN (
  5          SELECT prev_sql_id, prev_child_number
  6          FROM v$session WHERE sid = SYS_CONTEXT( 'userenv','sid' )
  7  );
  8  END;
  9  /

PL/SQL PROCEDURE successfully completed.

SQL> @ xpl1
SQL> SELECT * FROM TABLE( dbms_xplan.display_cursor( :sqlid1, :cld1, :xplanopts ));
SQL_ID  d4b6hf9535fdf, child NUMBER 0
-------------------------------------
SELECT pdt, a FROM p WHERE pdt = TO_DATE ( '20150425', 'yyyymmdd' )

PLAN hash VALUE: 102990640

-----------------------------------------------------------------------------------------------
| Id  | Operation              | Name | ROWS  | Bytes | COST (%CPU)| TIME     | Pstart| Pstop |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |      |       |       |     2 (100)|          |       |       |
|   1 |  PARTITION RANGE SINGLE|      |     1 |    14 |     2   (0)| 00:00:01 |     1 |     1 |
|*  2 |   TABLE ACCESS FULL    | P    |     1 |    14 |     2   (0)| 00:00:01 |     1 |     1 |
-----------------------------------------------------------------------------------------------

Predicate Information (IDENTIFIED BY operation id):
---------------------------------------------------

   2 - filter("PDT"=TO_DATE(' 2015-04-25 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))


19 ROWS selected.

SQL>
SQL> ALTER TABLE p
  2  ADD PARTITION p20150426 VALUES less than ( TO_DATE ( '20150427', 'yyyymmdd' ) );

TABLE altered.

SQL> INSERT INTO p ( pdt, a ) VALUES ( TO_DATE ( '20150426', 'yyyymmdd' ), 20150426 );

1 ROW created.

SQL>
SQL> COMMIT;

COMMIT complete.

SQL> EXEC dbms_stats.gather_table_stats(NULL,'p' );

PL/SQL PROCEDURE successfully completed.

SQL> SELECT pdt, a FROM p WHERE pdt = TO_DATE ( '20150426', 'yyyymmdd' );
20150426 00:00   20150426

SQL> @ phv2
SQL> BEGIN
  2  SELECT sql_id, child_number, plan_hash_value INTO :sqlid2, :cld2, :phv2
  3  FROM v$sql
  4  WHERE ( sql_id, child_number ) IN (
  5          SELECT prev_sql_id, prev_child_number
  6          FROM v$session WHERE sid = SYS_CONTEXT( 'userenv','sid' )
  7  );
  8  END;
  9  /

PL/SQL PROCEDURE successfully completed.

SQL> @ xpl2
SQL> SELECT * FROM TABLE( dbms_xplan.display_cursor( :sqlid2, :cld2, :xplanopts ));
SQL_ID  fq3ywc03zjnsv, child NUMBER 0
-------------------------------------
SELECT pdt, a FROM p WHERE pdt = TO_DATE ( '20150426', 'yyyymmdd' )

PLAN hash VALUE: 102990640

-----------------------------------------------------------------------------------------------
| Id  | Operation              | Name | ROWS  | Bytes | COST (%CPU)| TIME     | Pstart| Pstop |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |      |       |       |     2 (100)|          |       |       |
|   1 |  PARTITION RANGE SINGLE|      |     1 |    14 |     2   (0)| 00:00:01 |     2 |     2 |
|*  2 |   TABLE ACCESS FULL    | P    |     1 |    14 |     2   (0)| 00:00:01 |     2 |     2 |
-----------------------------------------------------------------------------------------------

Predicate Information (IDENTIFIED BY operation id):
---------------------------------------------------

   2 - filter("PDT"=TO_DATE(' 2015-04-26 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))


19 ROWS selected.

SQL> @ cmp
SQL> SELECT :sqlid1, :cld1, :phv1, :sqlid2, :cld2, :phv2, CASE WHEN :phv1 = :phv2 THEN 'SAME' ELSE 'DIFFERENT' END cmp FROM dual;
d4b6hf9535fdf                             0  102990640 fq3ywc03zjnsv                             0  102990640 SAME