XML structure change after updating data in XML

Hi experts,

Can you please help me with the problem regarding XML data updating. I have a problem that the structure of the XML changes after I make an update in XML.
Exactly: From

    <property id="32527" fileAssociated="0">
      <data>
        <string>NAE-01:NAE-01/MSTP_2.FX07_01.AV-0</string>
      </data>
    </property>

To:
    </property>
    <property id="32527" fileAssociated="0">NAE-01:NAE-01/MSTP_2.FX07_01nviTemp_Average</property>

I changed the inner string value and the structure is change also.

 I attached the code, the original and the updated XML file. What I'm doing wrong?
Thanx,

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Xml.Linq;
using System.Text;
using System.Windows.Forms;


namespace NAE_BACNet_Object_Change
{
    public partial class Main : Form
    {
        public Main()
        {
            InitializeComponent();
        }

        private void btnConvert_Click(object sender, EventArgs e)
        {
            XElement XObjectsElements = XElement.Load(@"export.xml");

            lstLog.Clear();
            string strFullReference = "";
            string strObjectName = "";

            foreach (XElement XObjectElement in XObjectsElements.Nodes().OfType<XElement>()) 
            {
                if ((string)XObjectElement.Attribute("classid") == "502" | (string)XObjectElement.Attribute("classid") == "519")
                {
                    foreach (XElement XPropertyElement in XObjectElement.Nodes().OfType<XElement>())
                    {
                        if ((string)XPropertyElement.Attribute("id") == "2390") { strObjectName = XPropertyElement.Value; }
                        if ((string)XPropertyElement.Attribute("id") == "32527")
                        {
                            strFullReference = XPropertyElement.Value;

                            int lastDotPosition = strFullReference.LastIndexOf('.');
                            string strNode = strFullReference.Substring(0, lastDotPosition);
                            string strObject = strFullReference.Substring(lastDotPosition + 1, strFullReference.Length - lastDotPosition - 1);

                            if (lastDotPosition != -1 && strObjectName != strObject)
                            {
                                lstLog.AppendText(String.Format("{0} -> {1}.{2}{3}", XPropertyElement.Value, strNode, strObjectName, Environment.NewLine));
                                XPropertyElement.SetValue(strNode + strObjectName);
                            }
                            else
                            {
                                lstLog.AppendText(String.Format("{0} -> {1}{2}", XPropertyElement.Value, "No Chnage", Environment.NewLine));
                            }
                        }
                    }
                }
            }
            XObjectsElements.Save(@"export.xml");
        }
    }
}

Select all Open in new window

export-original.xml
export-updated.xml