Bad IS NULL result on an expression containing a ROW SP variable

DELIMITER /

CREATE OR REPLACE PROCEDURE p1()

BEGIN

  DECLARE r0 ROW(a INT, b VARCHAR(10));

  DECLARE r2 ROW(a INT, b VARCHAR(10)) DEFAULT (1,'b1');

  SET r0=r2;

  SELECT '02' AS stage, r0=r2, (r0=r2) IS NULL;

END;

/

DELIMITER ;

CALL p1;

+-------+-------+-----------------+

| stage | r0=r2 | (r0=r2) IS NULL |

+-------+-------+-----------------+

| 02    |     1 |               1 |

+-------+-------+-----------------+

bool Field_row::sp_prepare_and_store_item(THD *thd, Item **value)

{

...

  src->bring_value();

  if (m_table->sp_set_all_fields_from_item(thd, src))

  {

    set_null();         // NEW

    DBUG_RETURN(true);

  }

  set_notnull();        // NEW

  DBUG_RETURN(false);

}