This implementation uses warehouse management. However a user was trying to fulfill the work without following the warehouse management fulfillment procedures.

Reason:
User posted picking list for 4 invenory units that work was already created for, and did not use warehouse management's work process to do this picking.

Steps needed to correct this issue:

1. Need to reduce the picked line quantity for the 4 that was not actually pack slip posted. To reverse it go to Sales Order > Action Pane > Pick and Pack > Picking List registration.
   Unpick each line.
2. 
3. Note: Screenshot taken from an unrelated order. Picking List Registration would be enabled in this scenario.
4. Then go to Inventory Management > Outbound Orders > Output Orders. Delete all the output orders.
5. 
6. With the output orders out of the way, you are now able to see the reservation against the sales line.
7. 
8. After doing this you will again see that the sales line is physically reserved. Sales Order > Action Pane > General > Line Quantity
9. Cancel any open work for this sales order line.

10. If you are unable to rerelease to the warehouse, then continue reading. The system still remembers the inventransId on the sales line, and you need to force the system to forget that inventTransID and get a new one. Go back to the sales order line and remove the reservation. A quick way to do this is to change the warehouse on the sales order line, and then change it back to the actual fulfillment warehouse.

11. Re-reserve inentory.

12. Now re-release to the warehouse.