WordML: w:hdr does not insert into existing document

[Michael]

Trying to insert a WordML fragment with a w:hdr into a document. If
the document is brand new and doesn't contain any content, it works
beautifully. However, if there is any content including just section
breaks, the InsertXML method will fire without an error but the
content is not inserted into the header.

In my research, I've come across mention that the w:sectPr (where
w:hdr is nested) can be treated as an optionally interpreted by Word.
Anyone else observe this or have a workaround?

Thanks!