Заменить текст в xml на заданный

Есть файл xml который имеет вид :

<?xml version="1.0" encoding="UTF-8"?>
<test title="This Xml will be updated">
    <line1>Xml has been renamed to New Xml</line1>
    <line1>Test has been renamed to Xml</line1>
    <line1>Xml has been renamed to Xml</line1>
    <line1>XmlXml has been renamed to New Xml</line1>
    <line1>Xml has been renamed to Xml</line1>
</test>

Нужно заменить добавить до всех слов Xml, слово New

Делаю так:

string prefix = "New";
string word = "Xml";
string regexPattern = $@"(?<!\b{prefix}\s+){word}\b";
string replacement = $"{prefix} $&";
XDocument xdoc = XDocument.Load(xmlFile.FullName);
foreach (var node in xdoc.Descendants())
{
    node.Value = Regex.Replace(node.Value, regexPattern, replacement);
    foreach (var attribute in node.Attributes())
    {
        attribute.Value = Regex.Replace(attribute.Value, regexPattern, replacement);
    }
}
return xdoc;

Замена происходит, но, почему то удаляются ноды <line1></line1> и xml становится в виде:

<?xml version="1.0" encoding="utf-8"?>
<test title="This New Xml will be updated">New Xml has been renamed to New XmlTest has been renamed to XmlNew Xml has been renamed to XmlXmlNew Xml has been renamed to New XmlNew Xml has been renamed to New Xml</test>

Что я делаю не так? В чем моя ошибка?