反序列化在WCF中不起作用

团队课看起来像

[DataContract]
public class Team
{
    [DataMember]
    public int Id { get; set; }
    [DataMember]
    public Point Position { get; set; }
    [DataMember]
    public string Code { get; set; }
    [DataMember]
    public bool Available { get; set; }
    [DataMember]
    public string Extra { get; set; }
    [DataMember]
    public double X { get; set; }
    [DataMember]
    public double Y { get; set; }
}

在客户端(Silverlight 3.0应用程序)上,我获得了所有数据,但Position属性保存了一个默认点实例。点结构是 System.Windows.Media.Point

截获的XML(谢谢,Firebug!)如下所示:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Body>
    <GetTeamsResponse xmlns="http://tempuri.org/">
        <GetTeamsResult xmlns:a="http://schemas.datacontract.org/2004/07/MyProject.Data" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
            <a:Team>
                <a:Code>A23HJGF23</a:Code>
                <a:Available>true</a:Available>
                <a:Extra i:nil="true"/>
                <a:Id>1</a:Id>
                <a:Position xmlns:b="http://schemas.datacontract.org/2004/07/System.Windows">
                    <b:_x>572194.59937858</b:_x>
                    <b:_y>322518.3889979</b:_y>
                </a:Position>
                <a:X>572194.59937858</a:X>
                <a:Y>322518.3889979</a:Y>
            </a:Team>
            <!-- other <a:Team> elements -->
        </GetTeamsResult>
    </GetTeamsResponse>
</s:Body>
</s:Envelope>

因此,似乎存在反序列化问题。

为什么?