Email subject: text placeholder is not replaced when order variable is also incl

-- HikaShop version -- : 4.7.4
-- Joomla version -- : 3.10.12
-- PHP version -- : 7.4.29

Hi,

I tried to add the order number to the email subject for the administrator notification email when an order is created but experienced the next:

1. When subject contains only text placeholder (or constant or I don't know what is the name of it in English) it works fine, the language specific expression is incuded
subject: ORDER_CREATION_NOTIFICATION_SUBJECT
result: "Új megrendelés történt az oldalán"

2.When the order number is addded to the subject, then it works partially, the text placeholder is not replaced to the language specific expression but the order number is filled:
subject: ORDER_CREATION_NOTIFICATION_SUBJECT - {order.order_number}
result: "ORDER_CREATION_NOTIFICATION_SUBJECT - 23/12/054160PB"

So it seems like if a DB field is included the text placeholders/constants are not processed.

Is there a way to make it work?

Best regards,

Bence