Bundling Styles doesn't work, but straight Link tag works

In my _Layout page, following works:

<link rel="stylesheet" href="@Url.Content("~/Kendo/Content/kendo/2013.2.918/kendo.common.min.css")"             />
<link rel="stylesheet" href="@Url.Content("~/Kendo/Content/kendo/2013.2.918/kendo.blueopal.min.css")"           />
<link rel="stylesheet" href="@Url.Content("~/Kendo/Content/kendo/2013.2.918/kendo.dataviz.min.css")"            />
<link rel="stylesheet" href="@Url.Content("~/Kendo/Content/kendo/2013.2.918/kendo.dataviz.blueopal.min.css")"   />

This doesn't work (the styles do get applied, however images referenced in the css don't render):

@Styles.Render("~/bundles/kendoStyle")

here's the Bundle def in App_start -> BundleConfig.cs:

        //Kendo Styles:
        bundles.Add(new StyleBundle("~/bundles/kendoStyle").Include(
          "~/Kendo/Content/kendo/2013.2.918/kendo.common.min.css"
        , "~/Kendo/Content/kendo/2013.2.918/kendo.blueopal.min.css"
        , "~/Kendo/Content/kendo/2013.2.918/kendo.dataviz.min.css"
        , "~/Kendo/Content/kendo/2013.2.918/kendo.dataviz.blueopal.min.css"
            //, "~/Kendo/Content/contextMenu.css"
        ));

What am I doing wrong here? (please note, "Kendo" is setup as an mvc4.5 web app under my main website