Hi,

in 'sale.order.line' :

_order = 'order_id desc, sequence'
_defaults = {      
            'sequence': 10,
            }

Sequence : Gives the sequence order when displaying a list of sales order lines.

so all order lines have a sequence=10.

to keep order of the input lines change _order by;

--  _order = 'order_id desc, sequence'
++  _order = 'id'

you can change it in sale.py but this is not the best way must create a new module to overwrite _order.