XMLdocument value changing automatically.

[rawatgaurav81]

I had this strange problem in handling XMLDocuments in asp.net.Though the problem occurs while working on the main application.I will try to explain it with shorter code.
I had a form with 2 buttons.The first button loads a file and second button make some changed in extracted XML node.The strange thing is that I am not touching the XMLdocument created in second button but still its getting changed.It will be more clear by seeing the examples.
The code behind for first button is :
protected void Button1_Click(o bject sender, EventArgs e)
{
XmlDocument xdcSettings = new XmlDocument();
string fileName = System.Configur ation.Configura tionSettings.Ap pSettings.Get(" RequestFilePath ") + "Settings.x ml";
xdcSettings.Loa d(fileName);
Session["Settings"] = xdcSettings;
Session["CurrentSetting "]=xdcSettings.Se lectSingleNode( "Settings/Setting[@id='S1']"); }

And for second button is :
protected void Button2_Click(o bject sender, EventArgs e)
{
XmlDocument xdcSettings = (XmlDocument)Se ssion["Settings"];
xdcSettings.Sav e(@"C:\Document s and Settings\gaurav .RC\Desktop\Set tingsBefore.xml ");
XmlNode xdc = (XmlNode)Sessio n["CurrentSetting "];
xdc["Elements"].InnerText = "101,102,10 3";
xdcSettings.Sav e(@"C:\Document s and Settings\gaurav .RC\Desktop\Set tingsAfter.xml" );
}

I am not able to understand how the variable xdcSettings in second button code is getting changed without me doing anything.The sample Settings.xml file is given as:
<Settings>
<Setting id="S1">
<Elements>101,1 02,103</Elements>
</Setting>
<Setting id="S2">
<Elements>5,6,7 ,8</Elements>
</Setting>
</Settings>
Is it because everything is being passed as reference and hance getting changed.Neverth eless still I am not sure how a standalone variable gets changed?