[Sienabird]

I began to set up my headers (in a book) to have a consistent even-page
header (book title) and an odd-page header with changing chapter titles. It
worked fine till a certain point -- at which suddenly all of the odd-page
headers changed to the latest one entered. Each chapter does begin with a
section break, and the header for each is marked "different first page" and
unlinked from the previous section. Each chapter title in the text is marked
"level 1."
I've done it over three times now, even saving the document after each
successful heading edit. But at a different point each round the same thing
happens. And if I then exit without re-saving, the file still comes up with
the same heading throughout!
Can anyone tell me what I'm doing wrong?