15-chapters carries what only a stylesheet holds: numbering on the heading
styles and two heading styles of the document's own. The round-trip legs now
carry that stylesheet too — a style the file names but the built-ins never
heard of can only be written from there — and one absolute assertion says the
chapters read as headings, which a round trip cannot: both its sides go
through the same importer, so a consistent misreading compares equal.
A numbered heading style rides the package's factory slot; a second definition
under the same id leaves two, and LibreOffice reads the first.
Steffen Becker
8b006d22a8