Online ALTER reports the number of affected rows incorrectly

--source include/have_debug_sync.inc

create table t (a int);

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

--send set debug_sync= 'now wait_for go_dml'

--connect (con1,localhost,root,,)

set debug_sync='alter_table_online_progress signal go_dml wait_for go_alter';

--send alter table t add b int, algorithm=copy, lock=none

--connection default

--reap

insert into t values (3);

set debug_sync= 'now signal go_alter';

--connection con1

--enable_info

--reap

--disable_info

select * from t;

# Cleanup

drop table t;

connect  con1,localhost,root,,;

set debug_sync='alter_table_online_progress signal go_dml wait_for go_alter';

alter table t add b int, algorithm=copy, lock=none;

connection default;

insert into t values (3);

set debug_sync= 'now signal go_alter';

connection con1;

affected rows: 2

info: Records: 2  Duplicates: 0  Warnings: 0

select * from t;

a	b

1	NULL

2	NULL

3	NULL