(Company Currency) in label is not working

I’ve added new field with a label Import Tax Amount (Company Currency) in Purchase Invoice Item DocType. Upon saving the document (ie. Purchase Invoice) the template string (Company Currency) of this field’s label is not changed by the actual company currency.

   "fieldname": "import_tax_amount",
   "fieldtype": "Currency",
   "label": "Import Tax Amount (Company Currency)",
   "options": "Company:company:default_currency"

Assuming the default currency is set to Nepalese Rupee I want the field label to change: Import Tax Amount (NPR) but it is displayed as Import Tax Amount (Company Currency).

Why is this happening only to my custom field? What should I do in order to get company currency value in field label ?

SS Attached:

I need some guidance here @bkm @ChillarAnand @brian_pond @peterg

I achieved this by adding following extension to the Purchase Invoice form.

frappe.ui.form.on('Purchase Invoice', {
    refresh(frm) {
        var company_currency = frappe.get_doc(":Company", frm.doc.company).default_currency;
        // Set currency lables on DocType
        // frm.set_currency_labels([
        //    "currency_label_1",
        // ], company_currency);

        // Set currency lables on Child Doc-Types
        ], company_currency, "items");