If you cancel a posted assembly order,

The following message may be displayed and you may not be able to cancel.

"The value of Unapplied Quantity must be equal to '9'.

Current value is 0. ”

To resolve the above issue, I canceled the Posted Sales Invoice for the item created with the Assembly Order, 

but the quantity that was supposed to have been received by the cancellation was not applied to the unapplied quantity.

If you perform adjustment receipt in the Item Journal, it will be applied to the unapplied quantity.

Why are the results of updating unapplied quantities different for canceling posted sales invoices and adjusting receipts for item journals?