ROW_NUMBER is wrong upon INSERT into Federated table

--source suite/federated/have_federatedx.inc

create table t (pk int primary key);

--eval create table tfed engine=FEDERATED connection='mysql://root@localhost:$MASTER_MYPORT/test/t'

--error ER_DUP_KEY

insert into tfed values (1),(2),(1);

get diagnostics condition 1 @val = error_index;

select @val;

# Cleanup

drop table tfed, t;

MariaDB [test]> insert into tfed values (1),(2),(1);

ERROR 1022 (23000): Can't write; duplicate key in table 'tfed'

MariaDB [test]> get diagnostics condition 1 @val = error_index;

Query OK, 0 rows affected (0.001 sec)

MariaDB [test]> select @val;

+------+

| @val |

+------+

|    4 |

+------+

1 row in set (0.001 sec)