Necesito un poco de ayuda con XmlSerializer. Tengo que seguir el fragmento xml:

<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet href="http://www.blogger.com/styles/atom.css" type="text/css"?>
<feed xmlns='http://www.w3.org/2005/Atom' xmlns:openSearch='http://a9.com/-/spec/opensearchrss/1.0/' xmlns:georss='http://www.georss.org/georss' xmlns:gd='http://schemas.google.com/g/2005' xmlns:thr='http://purl.org/syndication/thread/1.0'>
  <id>tag:blogger.com,1999:blog-4233645339430781865.archive</id>
  <updated>2012-10-22T07:00:02.139+03:00</updated>
  <title type='text'>Code !t</title>      
  <link rel='alternate' type='text/html' href='http://www.etabakov.com/'/>
  <author>
    <name>Емил Табаков</name>
    <email>[email protected]</email>
    <gd:image rel='http://schemas.google.com/g/2005#thumbnail' width='32' height='32' src='//lh5.googleusercontent.com/-TbRwL19G85U/AAAAAAAAAAI/AAAAAAAAFxg/NRV6ZYqd9Wg/s512-c/photo.jpg'/>
  </author>
  <generator version='7.00' uri='http://www.blogger.com'>Blogger</generator>
  <entry>
    <id>tag:blogger.com,1999:blog-4233645339430781865.post-513753811167440871</id>
    <published>2012-10-12T11:22:35.759+03:00</published>
    <updated>2012-10-12T11:22:35.759+03:00</updated>
    <category scheme='http://schemas.google.com/g/2005#kind' term='http://schemas.google.com/blogger/2008/kind#comment'/>
    <title type='text'>Great post indeed. I really like that you are prov...</title>
    <content type='html'>Great post indeed. I really like that you are providing information on .NET for freshers , Being enrolled  at http://www.wiziq.com/course/57-fresher-training-projects i found your information very helpful indeed. Thanks for it.</content>
    <link rel='edit' type='application/atom+xml' href='http://www.blogger.com/feeds/4233645339430781865/8317071019326278340/comments/default/513753811167440871'/>        
    <author>
      <name>sarabjeet</name>
      <uri>http://www.blogger.com/profile/11223974173581186160</uri>
      <email>[email protected]</email>
      <gd:image rel='http://schemas.google.com/g/2005#thumbnail' width='16' height='16' src='http://img2.blogblog.com/img/b16-rounded.gif'/>
    </author>
    <thr:in-reply-to href='http://www.etabakov.com/2012/06/net-guy-velocityconf-2012-day-1.html' ref='tag:blogger.com,1999:blog-4233645339430781865.post-8317071019326278340' source='http://www.blogger.com/feeds/4233645339430781865/posts/default/8317071019326278340' type='text/html'/>
    <gd:extendedProperty name='blogger.itemClass' value='pid-899300522'/>        
  </entry>
</feed>

Y también tengo los siguientes objetos c #:

Feed.cs

[XmlRoot(ElementName = "feed", Namespace = "http://www.w3.org/2005/Atom"), XmlType("feed")]
public class Feed
{
    [XmlElement("id")]
    public string Id { get; set; }

    [XmlElement("title")]
    public string Title { get; set; }

    [XmlElement("author")]
    public Author Author { get; set; }

    [XmlElement("entry")]
    public List<Entry> Entry;
}
public class Entry
{
    [XmlElement("id")]
    public string Id { get; set; }

    [XmlElement("title")]
    public string Title { get; set; }

    [XmlElement("content")]
    public string Content { get; set; }

    [XmlElement("published")]
    public DateTime Published { get; set; }

    [XmlElement("updated")]
    public DateTime Updated { get; set; }

    [XmlElement("category")]
    public List<Category> Categories;

    [XmlElement("author")]
    public Author Author { get; set; }

    [XmlElement(ElementName = "in-reply-to", Namespace = "thr", Type = typeof(ReplyTo), IsNullable = true)]
    public ReplyTo ReplyTo { get; set; }
}

public class ReplyTo
{
    [XmlAttribute("ref")]
    public string Id { get; set; }
}

Todo funciona perfectamente hasta ahora, excepto que la propiedad ReplyTo siempre permanece nula. Necesito obtener el atributo src de la

Estaré realmente feliz si alguien me muestra lo que me estoy perdiendo. ¡Gracias!