Theme Installer menu item is shown under Other but it cannot be run by the user since it takes a %u parameter. Version 2.19.x of gnome-control-center fixes the problem by setting ShowOnlyIn=; More information can be found here: http://bugzilla.gnome.org/show_bug.cgi?id=434956 Reproducible: Always
Created attachment 131968 [details, diff] control-center-2.18.1-menu.patch Backported patch to fix menu item visibility.
control-center-2.20.1 is stable by now, which has this fixed. Thanks for reporting