Replication stops with ERROR when Primary Key is not defined in Multi Master

Last_SQL_Error	Could not execute Delete_rows_v1 event on table test.t6; Can't find record in 't6', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log master-bin.000001, end_log_pos 0

--source include/have_innodb.inc

--let $rpl_topology= 1->2->1

--source include/rpl_init.inc

CREATE TABLE t6 ( id INT, a INT, b INT);

SET SESSION sql_log_bin=0;

ALTER TABLE t6 ADD COLUMN m1col INT AFTER a;

set session sql_log_bin=1;

--echo on server1

--query_vertical SHOW SLAVE STATUS

--source include/rpl_sync.inc

--let $rpl_connection_name= server_2

--source include/rpl_connection.inc

SET SESSION sql_log_bin=0;

ALTER TABLE t6 ADD COLUMN m2col INT AFTER a;

set session sql_log_bin=1;

INSERT INTO t6 VALUES(1,1,1,1);

INSERT INTO t6 VALUES(2,2,2,2);

SELECT * FROM t6;

--source include/rpl_sync.inc

--let $rpl_connection_name= server_1

--source include/rpl_connection.inc

SELECT * FROM t6;

INSERT INTO t6 VALUES(3,3,3,3);

INSERT INTO t6 VALUES(4,4,4,4);

--echo expect 4 rows

SELECT * FROM t6;

--source include/rpl_sync.inc

UPDATE t6 SET a=4 WHERE m1col=1;

--source include/rpl_sync.inc

--let $rpl_connection_name= server_1

--source include/rpl_connection.inc

DELETE FROM t6 WHERE m1col IS NULL;

--echo only 2 rows

SELECT * FROM t6;

--let $rpl_connection_name= server_2

--source include/rpl_connection.inc

--sleep 5

--echo DELETE FAILS HERE

--query_vertical SHOW SLAVE STATUS

./mtr rpl_multi_master --mariadbd=--binlog-format=ROW --mariadbd=--binlog-row-metadata=FULL