We notice backorder date for shipment is today.
We remark comment in code : # backorder can not be planned
In case of future sales, if customer is asking a part of ordered quantity sooner than excepted sale date the backorder shipment is planned on today.
Another case is, Sale with products having large lead time gap between them (product A 3 days lead time and product B 3 months lead time). The shipment is planned to the max shipping date = Sale date + lead time. If you ship the product A before the planned shipment date, the backorder with product B will be planned on today (without taking care of lead time).
Only in case of future sales, the backorder date should be the sale date with the lead time of the product.