Different first header not saving

using Version:, start a new document, I edit header format, selecting different first page header, apply, ok, write a header on page two. Format is correct. Save document as default RTF. Open document and it has changed to same header on page one. I have not found a way to edit header in a way that it will not revert to showing on first page every time I open it.
Is this a bug or am I missing something?

It’s a bug. Has been around forever. If you change pages styles on the Organizer tab of the page style dialog box (like in the First page style, which changes to Default for the next page), the page style change will not convert to RTF or the MS Word format. You have to insert a manual page break at the bottom of page 1 and set a different page style for page 2 (and following) to save it across file formats.

Try Tutorial on Page styles and headers/footers for more information.

One thing to add (unfortunately, it must be told again and again): DO NOT use foreign formats (RTF, DOC(X) etc.) for an ongoing/unfinished work. Save your documents to ODF only. And only after you have finalized a document, export it to anything else.