The patch
There is a serious backwards compatibilty (with older skins) problem in MediaWiki 1.18.1: 'headscripts' template data is set incorrectly when useHeadElement=false. This a) causes mediawiki.page.startup to not load and b) duplicates scripts which added with $wgOut->addScript(...).
The fix is very simple - 1-line patch in the attachment.
Version: 1.18.x
Severity: major
Attached: