negative Quantity Committed, Quantity on Hand changed for incorrect location

We have multiple inventory locations. We have Fulfill Based on Commitment set to Limit to Committed.

Using web services, we initialize a fulfillment from a sales order. Each sales order is allowed to have items from only one location. We add a packageList with tracking numbers to the fulfillment, add a custom note field, then update the sales order.

We were surprised when the new release would sometimes fail to save such fulfillments until we added a packageWeight that had not been required by previous release, but were able to resolve that issue.

Much more troubling is that sometimes when we save such a fulfillment, the quantity for one item shipped gets added to Quantity On Hand for the wrong location, and the Quantity Committed for the actual location becomes a negative number.