Office Interop Word Range.getXml(false) returning incorrect xml of the active document

I am working on an existing VSTO Project which is fetching the Xml of the active document using the following code:

object oMissing = System.Reflection.Missing.Value;
Document currentDocument = CAEGenieCommon.GenieEnvironment.CurrentDocument;
Range range = currentDocument.Range(ref oMissing, ref oMissing);
string contentXml = range.get_XML(false);

First, I can't find this method in the Range object on msdn in any version:

http://ift.tt/11Bp316

Second, this is not returning the correct xml of the active document, if the document is very large. When the document is large, it is missing the formatting/styling information from the paragraphs in the returned Xml.