write statistic is incremented for slaves

On a setup with two servers, the slave server's write statistic is incremented by either some command or a specific set of actions (unknown at this point). This is unexpected as nothing routed to a slave should be counted as a write.

Most likely a side-effect of the following commit from 2.5.11:

commit 2de10c9de12664e6d59f1ef879fd90d44b73d472

Author: Markus Mäkelä <markus.makela@mariadb.com>

Date:   Wed Apr 21 08:49:05 2021 +0300

    MXS-3468: Fix rwsplit query statistics

    The type of the query should determine whether the query is a write, not

    the target server where it ends up.