Hi everyone!
I'm working with 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

I'm trying to obtain json elements as columns in a view.
When I saw the plan for the following sql I realized that the cost increases when json_value is used more than once in the same column.

/*Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production*/

/*TESTING JSON_VALUE SELECTING FROM DUAL */
--COST OK
WITH Example AS(SELECT '{"element_1":"Radio controlled plane","element_2":"Ship"}' Json_1, '{"element_3":"Car","element_4":"Train"}' Json_2 FROM DUAL)
SELECT json_value(json_1,'$.element_1') element_1_value,json_value(json_1,'$.element_2') element_2_value,json_value(json_2,'$.element_3') element_3_value
FROM   Example A;



/*TESTING JSON_VALUE FROM EXAMPLE TABLE*/
drop table JSON_TEST;

CREATE TABLE JSON_TEST
(
  test_id number(4),
  JSON_1  VARCHAR2(100 BYTE),
  JSON_2  VARCHAR2(100 BYTE)
);

/*INSERT TEST DATA*/
Insert into JSON_TEST
   (test_id,JSON_1, JSON_2)
 Values
   (1,'{"element_1":"Plane","element_2":"Ship"}', '{"element_3":"Car","element_4":"Train"}');
   
Insert into JSON_TEST
   (test_id,JSON_1, JSON_2)
 Values
   (2,'{"element_1":"Duck","element_2":"Dog"}', '{"element_3":"Cat","element_4":"Mouse"}');

Insert into JSON_TEST
   (test_id,JSON_1, JSON_2)
 Values
   (3,'{"element_1":"Glass","element_2":"Knife"}', '{"element_3":"Bottle","element_4":"Cup"}');
   
      
COMMIT;

/*TESTING COST WITH ONLY ONE ELEMENT FROM EACH JSON COLUMN (JSON_1, JSON_2)*/
--COST OK
SELECT json_value(json_1,'$.element_1') element_1_value,json_value(json_2,'$.element_3') element_3_value
FROM   JSON_TEST ;

/*TESTING COST WITH TWO ELEMENTS FROM ONE JSON COLUMN (JSON_1)*/
--COST INCREASES A LOT, JSONTABLE EVALUATION IS NOW PRESENT IN THE PLAN
SELECT json_value(json_1,'$.element_1') element_1_value,json_value(json_1,'$.element_2') element_2_value
FROM   JSON_TEST ;

There's a bug or i'm doing something wrong?
How can I or our DBA's fix this problem?

Thanks!!

SELECT 
  json_value(json_1,'$.element_1') element_1_value,
  json_value(json_1,'$.element_2') element_2_value 
FROM   JSON_TEST ;

select p.c_02$ element_1_value,p.c_01$ element_2_value 
from json_test json_test,
  json_table( json_test.json_1, 
    '$' columns( c_01$ varchar2(4000) path '$.element_2' null on error , 
                 c_02$ varchar2(4000) path '$.element_1' null on error ) 
  )  p