Why the equipment disappear of the inventory asset, when is unassign to shipment?

Hi All!

I have a problem with my inventory Asset, when I unassign all (driver, equipment and equipment type) to the shipment, the Equipment disappear to the inventory asset for the location, so when I try to assign a new shipment. So, I have to add again the equipment an inventory.

Why the equipment disappear of the inventory asset, when is unassign to shipment?

Thank you!