Unable to set item group component quantity through setting item group parent quantity via Script

Hello,

I'm unable to set item group component quantity through setting item group parent quantity via Script, here is my example code:

function TransformRecordSetLineQuantitySS() {

    var invoice = nlapiTransformRecord('salesorder',39489, 'invoice');

    invoice.setLineItemValue('item', 'quantity', 1, 20);

    nlapiSubmitRecord(invoice);

}

Here is the Sales Order lines:

Here is the transformed Invoice:

as you can see the item group parent quantity is changed by the script correctly, but the components quantity does not change respectively.

Could you please let me know a potential solution for this. The behavior of the system is correct and as expected on the UI.