Custom product layout is not applied to product variants

-- url of the page with the problem -- : www.abibannerdrucken.de/
-- HikaShop version -- : 4.4.0
-- Joomla version -- : 3.9.24
-- PHP version -- : 7.4
-- Browser(s) name and version -- : Google Chrome 88.0.4324.104

Dear Hika-Shop-Team,

first of all: Thank you for your work and the great software you are developing in such a great way! Its working so fantastic, except one thing: I have created a custom product page layout called show_qm (mainly a copy of show_default but refers to a different listing_price-view, where I have inserted another name for the PER_UNIT-translation (now its PER_QM)). This view works fine on all main-products. But if I change the product to one of its child from the options menue, the view is not applied anymore (so in my case the PER_QM-translator changes back to PER_UNIT). I also have tried to insert the product-layout-name directly in the database.

Inside the DB-table hikashop_product there is a column named product_layout. But it seems like only the main-products are using this table to get their product-layout-information, because if i enter show_qm in a variant product there, nothing changes.

So my question is, where can I find the PHP-part that loads the Variants from database? I quess I have to add / change a few lines of code to get Hika-Shop read the database-column "product layout" when loading the product variants. Or is there any other way?

Thank you very much,
best regards
Niclas