Error updating XML file on Android

I'm trying to edit an XML file on Android and when I do the update, if the String that I'm adding to a node is greater than the one by default, my XML becomes corrupted.

If I have:

<Configuracion>
  <CamposEditables>Empresa</CamposEditables>
</Configuracion>

and I add ", Web" to the node I get:

<Configuracion>
  <CamposEditables>Empresa, Web</CamposEditables>
</Configura

I've added 5 chars to a node but my file keeps having the same name of chars so it takes 5 chars from the end of the file.

Here is my code:

File filexml = new File(Environment.getExternalStorageDirectory().getAbsolutePath().toString() + "/configuracion.xml");

DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder;
dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(filexml);
doc.getDocumentElement().normalize();

updateElementValue(doc, camposeditables);

doc.getDocumentElement().normalize();
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(filexml);
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.transform(source, result);

and:

private static void updateElementValue(Document doc, String txt) 
{
    NodeList config = doc.getElementsByTagName("Configuracion");
    Element emp = null;
    for(int i=0; i<config.getLength();i++){
        emp = (Element) config.item(i);
        Node name = emp.getElementsByTagName("CamposEditables").item(0).getFirstChild();
        name.setNodeValue(txt);
    }
}

Thanks in advance for the help you can give me.