Last modified: 2013-07-15 04:28:00 UTC
uls-previous-languages is set separately for each path (e.g. /wiki and /w), which means they become inconsistent. After bug 49154 is fixed, it should use wgCookiePath for the path.
In the meantime, in resources/js/ext.uls.init.js change $.cookie( mw.uls.previousLanguagesCookie, $.toJSON( previousLanguages ) ); to $.cookie( mw.uls.previousLanguagesCookie, $.toJSON( previousLanguages ), { path: '/' } ); I submitted https://gerrit.wikimedia.org/r/#/c/73506/ , for some reason this bug isn't getting updated.
Gerrit change #73506 merged