Hello,
The feature do not change the behavior of the "namebox" system, the user can still select any category he wants.
But the option should perform a filtering and remove all new categories which are not leaf categories.
I checked the code and saw that there was a regression in recent release.
Please edit the file "administrator/components/com_hikamarket/classes/product.php" and replace the lines
$keepCategories = array_intersect($categories, $oldCategories);
$addedCategories = array_intersect($categories, $leafCategories);
By
$keepCategories = array_intersect($product->categories, $oldCategories);
$addedCategories = array_intersect($product->categories, $leafCategories);
It should restore the filtering while saving the product.
Regards,