Last modified: 2014-08-29 11:43:12 UTC
I'm fairly sure it is in OutputPage::addMeta(). My reason for thinking there is a problem is that the extension MetaDescriptionTag (http://www.mediawiki.org/wiki/Extension:MetaDescriptionTag) works fine in 1.16.1 (in MonoBook derivatives) and prior 1.16, and also works just fine in the latest 1.18 svn builds. However, in 1.16.1 when using a Vector derivative the new tag is parsed but not actually output to a page. Hope this is enough of a description.
Switching component to Vector skin since the error seems skin-specific. Since it works in trunk, presumably this is something that was fixed since the 1.16 branch but was never merged back.
1.16 is no longer supported, and this works on newer versions per comment 0.