As of r84905 [1] (going live to Wikimedia within the hour), the cltype parameter to list=categorymembers is ignored when clsort=timestamp is set. This change is needed for performance reasons: long-running queries were causing bug 28291 [2] on Wikimedia wikis. This does not break backwards compatibility with any released version of MediaWiki, because cltype is new in 1.17. Functional cltype=foo&clsort=timestamp behavior was only live on Wikimedia wikis for about 2-3 weeks. Roan Kattouw (Catrope)