joomla/joomla-cms — pull request #2669 by jacob87o2 (2013-12-11 17:13:20+00:00)
Title: Adding "active" and "current" classes to Article Categories Module list items

A byway solution to this problem:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32922&start=0

Not very elegant, needs refactoring.