The 'cmnamespace' parameter to the 'categorymembers' query has been disabled in miser mode, which has the effect of disabling it on WMF wikis. The parameter is simply ignored, causing category lists to include pages in all namespaces. The simplest workaround is to filter category lists locally.
References: * http://www.mediawiki.org/wiki/Special:Code/MediaWiki/53052 * https://bugzilla.wikimedia.org/show_bug.cgi?id=19640
- Carl