optimize table: Query could not be tokenized/Parsing the query failed, cannot report query type

optimize table <tab> throws error (client):
MariaDB [****]> optimize table ****;
ERROR 1141 (HY000): Access denied for user '****'@'::ffff:****': Query could not be tokenized and will hence be rejected. Please ensure that the SQL syntax is correct.

maxscale-log:
2018-12-20 15:48:23 info : (5) [qc_sqlite] Parsing the query failed, cannot report query type: optimize table ****
2018-12-20 15:48:23 warning: (5) [dbfwfilter] Query could not be tokenized and will hence be rejected. Please ensure that the SQL syntax is correct: optimize table ****

when using dbfwfilter and rules containing regex
no regex-rules: optimize table works.