Remove the pricelist_id assignment (leave the default one) because it may fail
if the user does not have the product.group_product_product_pricelist group
Into the normal process of the invoice creation from a sale order by odoo, the onchange_partner is called. In some case, this call will reset the specific payment_mode and/or partner_bank_id set on the sale_order.
To fix this issue, we must override the _finalize_invoices method, take a snapshot of these values before the call to super and restore these values if these are changed.
fixes#536
