Last modified: 2014-05-21 10:45:47 UTC
662d6f93b0156bdaab67f74dfd5fecf4ed739f01 added a GRAMMAR usage to guidedtour-tour-firsteditve-edit-page-description (among others). Using {{ had the side effect of causing jQueryMsg to start parsing it, instead of mediawiki.js's bare-bones message parser. jQueryMsg apparently does not handle HTML entities.
Change 134516 had a related patch set uploaded by Mattflaschen: Fix exposed markup https://gerrit.wikimedia.org/r/134516
Change 134516 merged by Phuedx: Fix exposed markup https://gerrit.wikimedia.org/r/134516