Joining took each card's cars in stored order and turned the lot by the
first card's flag, so a turned card came out reversed; splitting gave every
car the unit's flag. Both now go by the running order, and the coupler sides
by each car's own facing, which is what the export writes.
Randomising flipped only the card's flag, so a multi-car unit was exported
with its cars in reverse order but each still facing forward - coupled back
to front. A swap copied the flag without turning the new cars. Both now turn
flag, cars and order together, as Flip does, and a locked unit as one.
