An update on https://gist.github.com/frankgeerlings/1711560 MVC doesn't like the missing trailing slash on the URI authority (empty path), it's against HTTP/1.1 requirements as well it seems.

gistfile1.cs

    // Put this in Global.asax.cs

    protected void Application_BeginRequest(object sender, EventArgs e)
    {
        // Do Not Allow URL to end in trailing slash
        string url = HttpContext.Current.Request.Url.AbsolutePath;
        if (string.IsNullOrEmpty(url) 
            || url.Trim() == "/" 
            || url.Trim() == "\\") return;

        string lastChar = url[url.Length - 1].ToString();
        if (lastChar == "/" || lastChar == "\\")
        {
            url = url.Substring(0, url.Length - 1);
            Response.Clear();
            Response.Status = "301 Moved Permanently";
            Response.AddHeader("Location", url);
            Response.End();
        }
    }