main.multi_update_debug failed in buildbot with debug sync point wait timed out

main.multi_update_debug                  w1 [ fail ]

        Test ended at 2019-07-15 08:39:48

CURRENT_TEST: main.multi_update_debug

--- D:/win32-debug/build/src/mysql-test/r/multi_update_debug.result	2019-07-15 08:07:05.143117000 +0000

+++ D:\win32-debug\build\src\mysql-test\r\multi_update_debug.reject	2019-07-15 08:39:47.822875200 +0000

@@ -9,5 +9,7 @@

 update t1 join t2 on (a=c+4) set b=d;

 set debug_sync='mdl_acquire_lock_wait SIGNAL cont';

 lock table t1 write, t0 write;

+Warnings:

+Warning	1639	debug sync point wait timed out

 drop table t1, t2, t0;

 set debug_sync='reset';

mysqltest: Result length mismatch