Overhead getting calculated multiple times when using Origin groups in Costing sheet

[Soami]

We are Planning to use Origin Groups in Material master for Tariff on Materials imported.

We have created origin Groups for 10 countries for testing and assigned to Origin groups to imported raw materials.

We have also created new Calculation Base in our costing sheet with cost element group and Origin group as below:

For this calculation base,  we have assigned a OH rate. 

When we run costing run (CK11N) for Raw material A  the OH rate for tariff is coming correctly and overhead amount is calculated correctly. But when we do costing run (CK11N) for Finished product using Raw material A then SAP again shows the tariff overhead on the Raw material A . So the Tariff overhead is getting calculated TWICE. 

Please confirm how we can avoid this Duplicate calculation.