Re: Newly added tags being converted to OpenXmlUnknownElement when saved

I am reading in a document in C# and adding Tags to a few elements.  I am then calling MainDocumentPart.Document.Save(), and am serializing the document back into a byte array to be used at a later time.  Unfortunately, when I deserialize said byte array back into a document again, all of my Tags are now OpenXmlUnknownElements.  Is there some other part besides MainDocumentPart.Document that I need to call Save() on?

I met the same problem!!!
this problem also occurs when you set the InnerXml property of an OpenXmlElement...
the descendants all turn into OpenXmlUnknownElement!!