2 ETO Parent/Child works orders

I have 2 WO where the child WO was issued to the parent WO before the child WO was completed. The issue to the parent WO was at zero cost. When the child WO was completed the IC had a value. A 2nd IC transaction has been created which only has a value which basically brings the value of the IC to zero. Why would this be? I would have thought that the IC with a unit cost would have updated the cost of the item.