Sales order ATP gives way to Subcontracting stock transfer posting

[Former Member]

Hi Gurus,

Material ABC is a subcontracting part that will be supplied to Vendor and also will be Sold to customers at the same time.

Scenario: Material ABC has stock 500 EA. I created a Sales Order for 500 EA, ran ATP and the Sales order has confirmed schedule line, then activated fixed qty indicator. Later I created a PO and added Material ABC as a Subcontracting part and performed ATP check, result is 'no stock' to confirm.

But when I do MB1B, Mvt 541 (Transfer posting) it moves the stock to Vendor and Sales Order automatically loses the confirmation.

ATP settings: same as '02' expect that 'W/o subcontracting' is active on 'A' and 'BO'.

Please help me understand, how I can prevent MB1B stealing stock from a confirmed Sales order.