How does the DEMAND_PHYS_INV table get populated when doing an Express Issue

Does anyone know how the DEMAND_PHYS_INV table gets populated via an express issue? We are noticing express issues getting stuck in a Shipped state and will not deplete when running the depletion process. All of the express issues that are stuck in this state do not have a row populated on the DEMAND_PHYS_INV table which we think is part of the problem. This issue appears to be sporadic as it does not happen to every express issue or specific items. We are trying to figure out where the insert into DEMAND_PHYS_INV occurs if it's from an express issue.