Couple of suggestion
a. Try doc.Package.Flush(); after you write the data back into the custom xml.
b. You may have to delete all custom part and add a new custom part. We are using the following code and it seems working fine.
public static void ReplaceCustomXML(WordprocessingDocument myDoc, string customXML)
{
MainDocumentPart mainPart = myDoc.MainDocumentPart;
mainPart.DeleteParts<CustomXmlPart>(mainPart.CustomXmlParts);
CustomXmlPart customXmlPart = mainPart.AddCustomXmlPart(CustomXmlPartType.CustomXml);
using (StreamWriter ts = new StreamWriter(customXmlPart.GetStream()))
{
ts.Write(customXML);
ts.Flush();
ts.Close();
}
}
public static MemoryStream GetCustomXmlPart(MainDocumentPart mainPart)
{
foreach (CustomXmlPart part in mainPart.CustomXmlParts)
{
using (XmlTextReader reader =
new XmlTextReader(part.GetStream(FileMode.Open, FileAccess.Read)))
{
reader.MoveToContent();
if (reader.Name.Equals("aaaa", StringComparison.OrdinalIgnoreCase))
{
string str = reader.ReadOuterXml();
byte[] byteArray = Encoding.ASCII.GetBytes(str);
MemoryStream stream = new MemoryStream(byteArray);
return stream;
}
}
}
return null; //result;
}
using (WordprocessingDocument myDoc = WordprocessingDocument.Open(ms, true))
{
StreamReader reader = new StreamReader(memStream);
string FullXML = reader.ReadToEnd();
ReplaceCustomXML(myDoc, FullXML);
myDoc.Package.Flush();
//Code to save file
}