I have never had this issue, when Mobile Data is toggled off, the mobile data (4G, 3G, 1X) symbol goes away completely from the notification bar, as well as when WiFi is connected. Is the mobile network actually turning off? If you go to the settings menu and look at it does it say "Turning off...", "Turning On...", Connect to the Internet", "Connected" or something else under the words Mobile network in the menu?