Hello,
This is standard behaviour for Assemble-to-Order. When the item is ATO, Business Central creates a one-to-one link between the sales order line and the assembly order, plus an automatic reservation between the sales demand and assembly supply; that is why cancelling the reservation is blocked with Disallow Cancellation = Yes. In standard BC, you should not treat that reservation like a normal stock reservation, because it is what keeps the sales line, assembly output, and shipment tied together. For your questions: de-linking the assembly order while keeping it as-is is not really a standard flow; you would normally change/delete the ATO quantity/order or use a standalone assembly order, otherwise you are into customization. Partial shipment is supported, but the key rule is that ATO quantity is controlled through Qty. to Ship / Quantity to Assemble, and BC expects the required assembly components/output to be available for the quantity being shipped; it will not ship an ATO line just because the customer allows partial shipment if the assembly side cannot be posted. So your workaround of using a standalone assembly order is the clean standard approach; if the customer wants to freely break the link and manage reservations manually, that is a customization/design change.
Regards,
Oussama Sabbouh
