Ad nedostatek OS je ze dovolej umistit okno mimo viditelnou plochu - API to zjevně umožňuje i na Linuxu a MacOS X. Jinak by si na to uživatelé nestěžovali:
http://stackoverflow.com/questions/12477435/window-appears-off-screen-on-ubuntu
http://superuser.com/questions/55341/move-an-off-screen-window-back-on-screen-on-mac-os-x