The Formula dialog gains the number format Word's has: whole numbers, two
decimals, grouped thousands and the two percentages beside the general
one.
ODF keeps it on the cell *style* as a reference to a data style — odf-kit
shares one cell style across every cell, so a formatted cell gets a copy
of it — and LibreOffice writes both back unchanged. Word keeps it on the
field as its \# switch; LibreOffice's DOCX filter neither reads nor writes
that switch, so that leg holds through our own round trip.