plugins.processlist fails in buildbot with syntax error

plugins.processlist 'innodb_plugin'      w3 [ fail ]

        Test ended at 2018-07-19 03:17:20

CURRENT_TEST: plugins.processlist

mysqltest: At line 13: query 'select regexp_replace("$s", '(?s)^.*MySQL thread id $id,.*root([^\n]*)\n.*', '\\\\1') as `state from show engine innodb status`' failed: 1064: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ';;

 2: len 7; hex 9d0000023e0110; asc     >  ;;

 3: len 4; hex 80000001; asc    ' at line 1

The result from queries just before the failure was:

create table t1 (a int) engine=innodb;

start transaction;

insert t1 values (1);