Thread:Extension talk:Vector/My left menu won't collapse

I have installed the extension as described, I have inserted the necessary text into local.php, yet the menu won't collapse. Stranger yet: I have 2 wikis: collapsible menu works in one wiki, but not int the other. Same extensions installed, same localsettings.php. Could there be some problem with style sheets? I have differences there. Thanks for any tip. Anja