I'm almost certain I've given the answer to
this one out twice; you
refer to your own Skin derivative, which can therefore override the
Skin::getCategoryLinks() method to construct a real list
I know you did - but I
still can't get it done.
I've had some help with this issue, and am happy (and relieved) to
proclaim that this has been fixed now.
Apparently the key was to use "$skin = $wgUser->getSkin();"...