Comment 3 for bug 283229

10:11 apachelogger_ davmor2, Riddell: I don't think the problem lies within KDE
  10:11 apachelogger_ system and settings are both main categories, IMHO this behavior is to be expected
  10:12 apachelogger_ about main categories "By including one of these categories in an application's desktop entry file the application will be ensured that it will show up in a section of the application menu dedicated to this category."
  10:12 apachelogger_ sounds like ksycoca does exactly what the spec say

Also see http://standards.freedesktop.org/menu-spec/menu-spec-1.0.html for reference.