hikashop mini cart doesn't stay mini

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.5
-- PHP version -- : 5.5.30

I've configurated my module cart as a mini cart - only one record with:

2 items for €24

But when I add a new products, my mini cart doesn't stay mini but it shows as one record per product, like
item 1 €12
item 2 €12
item 3 €12

Then, when I do a refresh, my mini cart is mini again:

3 items for €36

I want it to stay mini, how do I prevent what happens when you place something new in the cart?

regards

Suzanne