binlog_encryption.encrypted_master failed in buildbot with WSREP warnings

binlog_encryption.encrypted_master 'cbc,innodb,stmt' w4 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2017-10-19 04:58:42

line

2017-10-19  4:58:42 70367360286720 [Warning] WSREP: binlog trx cache not empty (210 bytes) @ connection close 11

2017-10-19  4:58:42 70367360286720 [Warning] WSREP: binlog stmt cache not empty (191313 bytes) @ connection close 11

^ Found warnings in /dev/shm/var/4/log/mysqld.1.err

ok

 - skipping '/dev/shm/var/4/log/binlog_encryption.encrypted_master-cbc,innodb,stmt/'

Retrying test binlog_encryption.encrypted_master, attempt(2/3)...