Why doesn't IE recognize my output as XML?

I built the following code to output XML:

    public static XDocument Serialize<T>(this T source) where T : class
    {
        XDocument document = new XDocument();
        XmlReflectionImporter xmlReflection = new XmlReflectionImporter();
        XmlTypeMapping xmlMapping = xmlReflection.ImportTypeMapping(typeof(T));
        XmlSerializer xmlSeri开发者_StackOverflow中文版alizer = new XmlSerializer(xmlMapping);

        using (XmlWriter xmlWriter = document.CreateWriter())
            xmlSerializer.Serialize(xmlWriter, source);

        return document;
    }

Then in one of my aspx pages I have the following output:

    XDocument output = GetSomeXmlSerializedOutput();
    output.Save(Response.OutputStream);  

GetSomeXmlSerializedOutput() is basically output from feeding a class to the Serialize extension method.

The page's header looks like this:

<%@ Page Language="C#" CodeBehind="Alerts.aspx.cs" Inherits="Infinix.Diageo.WebApp.Get.Alerts" ContentType="text/xml" %>

Firefox correctly assumes from just the ContentType that the output is XML. IE doesn't. The output XML, for reference, is:

<?xml version="1.0" encoding="utf-8"?>
<ALERTS xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ALERT>
    <ID>1</ID>
    <TYPE>ALERT</TYPE>
    <NAME>neim</NAME>
    <DETAIL>diteil</DETAIL>
    <DATE>11/28/2010</DATE>    
    <TIME>13:50:02</TIME>
  </ALERT>
  <ALERT>
    <ID>2</ID>
    <TYPE>EVENT</TYPE>
    <NAME>iven</NAME>
    <DETAIL>ditel</DETAIL>    
    <DATE>11/28/2010</DATE>
    <TIME>13:50:15</TIME>
  </ALERT>
  <ALERT>
    <ID>3</ID>
    <TYPE>BIRTHDAY</TYPE>
    <NAME>pijazo</NAME>    
    <DETAIL>grande!</DETAIL>
    <DATE>11/28/2010</DATE>
    <TIME>13:50:23</TIME>
  </ALERT>
</ALERTS>

Why doesn't IE recognize this output as genuine XML?

Your page directive needs to set the ContentType="application/xml".

<%@ Page Language="C#" CodeBehind="Alerts.aspx.cs"
    Inherits="Infinix.Diageo.WebApp.Get.Alerts" ContentType="application/xml" %>