A flaw was found in Mediawiki before 1.28.1 / 1.27.2 / 1.23.16. Affected versions contains a flaw making rawHTML mode apply to system messages. References: https://phabricator.wikimedia.org/T156184 https://lists.wikimedia.org/pipermail/mediawiki-announce/2017-April/000207.html
Created mediawiki123 tracking bugs for this issue: Affects: epel-7 [bug 1569797]