main.delete_use_source fails sporadically in buildbot with wrong execution plan

main.delete_use_source 'innodb'          w2 [ fail ]

        Test ended at 2017-08-01 13:18:28

CURRENT_TEST: main.delete_use_source

--- /usr/share/mysql/mysql-test/r/delete_use_source.result	2017-08-01 08:31:50.000000000 -0400

+++ /dev/shm/var/2/log/delete_use_source.reject	2017-08-01 13:18:27.839087197 -0400

@@ -44,8 +44,8 @@

 start transaction;

 explain delete from v1 where (select count(*) from t1 b where b.c1=v1.c1) = 500 limit 1;

 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

-1	PRIMARY	t1	range	c1	c1	4	NULL	550	Using where

-2	DEPENDENT SUBQUERY	b	ref	c1	c1	4	test.t1.c1	82	Using index

+1	PRIMARY	t1	ALL	c1	NULL	NULL	NULL	472	Using where

+2	DEPENDENT SUBQUERY	b	ref	c1	c1	4	test.t1.c1	113	Using index

 delete from v1 where (select count(*) from t1 b where b.c1=v1.c1) = 500 limit 1;

 affected rows: 1

 delete from v1 where (select count(*) from t1 b where b.c1=v1.c1) = 500 limit 1;

@@ -60,8 +60,8 @@

 start transaction;

 explain delete from v1 where (select count(*) from t1 b where b.c1=v1.c1) = 500;

 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

-1	PRIMARY	t1	ALL	c1	NULL	NULL	NULL	717	Using where

-2	DEPENDENT SUBQUERY	b	ref	c1	c1	4	test.t1.c1	82	Using index

+1	PRIMARY	t1	ALL	c1	NULL	NULL	NULL	472	Using where

+2	DEPENDENT SUBQUERY	b	ref	c1	c1	4	test.t1.c1	113	Using index

 delete from v1 where (select count(*) from t1 b where b.c1=v1.c1) = 500 ;

 affected rows: 500

 select count(*) from v1 where c1=0;

mysqltest: Result length mismatch