Help with bundling and minification

Hi I have the following files in my solution along with the register css method. I am updating bootstrap-responsive.css in VS and saving it. However, how and when is the min version supposed to be updated? It does not seem to get updated. I have built and published and checked. Can anyone help with this?

bootstrap-responsive.css
bootstrap-responsive.min.css

private static void RegisterStyleBundles(BundleCollection bundles)
{
bundles.Add(new StyleBundle("~/css")
.Include("~/Content/bootstrap.css")
.Include("~/Content/bootstrap-responsive.css")
.Include("~/Content/site.css")
.Include("~/Content/thebigidea.css"));
}

EDIT: In fact I just checked and the bootstrap-responsive.css is actually minified. So whats the point of the bootstrap-responsive.min.css file? The other file seems to all you need?

Thanks.