Vaadin Touchkit iOS Splash Screen (Startup Image) not showing

I have implemented a small Mobile Interface for my Application.
As I followed the Coding instructions I implemended a Startup Image like this: 

@WebServlet("/*")
public class RKServlet extends TouchKitServlet {

    @Override
    protected void servletInitialized() throws ServletException {
        super.servletInitialized();

        String contextPath = getServletConfig().getServletContext().getContextPath();

        getTouchKitSettings().getWebAppSettings().setStartupImage(contextPath + "/VAADIN/themes/rkordering/startup.png");
        getTouchKitSettings().getWebAppSettings().setWebAppCapable(true);
        getTouchKitSettings().getViewPortSettings().setViewPortUserScalable(false);
        getTouchKitSettings().getWebAppSettings().setStatusBarStyle("black-translucent");
        getTouchKitSettings().getApplicationIcons().addApplicationIcon(contextPath + "/VAADIN/themes/rkordering/images/oerk_large.png");
        getTouchKitSettings().getApplicationIcons().addApplicationIcon(contextPath + "/VAADIN/themes/rkordering/images/oerk_medium.png");
        getTouchKitSettings().getApplicationIcons().addApplicationIcon(contextPath + "/VAADIN/themes/rkordering/images/oerk_small.png");

        getService().addSessionInitListener(new SessionInitListener() {
            @Override
            public void sessionInit(SessionInitEvent event) throws ServiceException {
                event.getSession().addUIProvider(new RKUIProvider());
            }
        });
    }
}

I added the Application to my home screen (iOS Webapp feature) but as you can imagine from the topic title, the Startup image is never shown.
Although, all Application Icons work properly...

I have no Idea what's exactly wrong!
Happy for any advise ... Thanks