Why does the pick release transaction erases the pick from subinventory when the shipment is typed?

Summary:

At the moment of the pick release, as i put the shipment number in the rule paramenters, the system erases the pick from subinventory that was defaulted from the rule, the user has to type it again (Thats a rework for us because if the pick form subinventory was defaulted by the rule, why does the user has to type it again). The question is:
At the moment of the pick release, can i poblate the shipment filed in the demand selection work area a without the system erasing the pick from subinventory form the Options work area?

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