When a sales order is closed, through reason of rejection, the product allocation entries in DP planning book are released for the given characteristic combination.
How does it happen technically i.e. what are the entries which it deletes?
Does product allocation group come into picture ?
When you set a reason for rejection and save the order a "ATP check" happens which release the quantity. When the queue update is processed in APO the system finally deletes the qty from the allocation tables and planning area.
The allocation consumption is stored in allocation table /SAPAPO/SDQTVB (you can access the table via the POSGUID from /SAPAPO/POSMAPN).