Why Additional output transaction are not costed if the work order is not closed?

Why Additional output transaction are not costed if the work order is not closed?

Even though the primary output shows as Fully Costed the Additional outputs appear Not Costed and Shows below error.

This scenario comes into picture when we have a long running job which is completed over a period of time and hence it is important to cost the actual consumptions and completions as and when required to capture the correct cost.