Incorrect v$parameter isdefault = true

SQL> set linesize 300
SQL> column ksppstvl format a30
SQL> select indx from x$ksppi where ksppinm ='optimizer_features_enable' and con_id = 1;

      INDX
----------
      2740

SQL> select ksppstdf, ksppstvl from x$ksppcv where indx = 2740;

KSPPSTDF  KSPPSTVL
--------- ------------------------------
TRUE      12.1.0.2

SQL> alter session set optimizer_features_enable = '12.1.0.1';

Session altered.

SQL> select ksppstdf, ksppstvl from x$ksppcv where indx = 2740;

KSPPSTDF  KSPPSTVL
--------- ------------------------------
TRUE      12.1.0.1

SQL> column value format a30
SQL> select isdefault, value from v$parameter where name ='optimizer_features_enable' and con_id = 1;

ISDEFAULT VALUE
--------- ------------------------------
TRUE      12.1.0.1