When i add to cart a multiple product changing the quantity the asked quantity is carried only in the first item of all items grouped in the multiple products.
I think it would be better to carry the asked quantity into all items grouped into the multiple product (or at least do not carry any quantity into all the items grouped into the multiple product)
Тhank you for your suggestion!
Actually we can use only one of the multiple products to build the quantity box as we can't use both or if there are more.
I will give you an example. Let's say you have 2 associated products and the first one has a minimum quantity of 3 and the second one has a specified list of available quantities i.e 2, 4 ,6 etc. On that catalog page we always use the first associated product and we will show quantity 3 by default in the quantity box and this number does not make sense for the second product.
So that is why we do not try to carry the same quantity to all products as it may not make sense for them.
Hope this makes sense!