1 Item in grouped Item is not added

I created a grouped item
Item 1: quantity selectable
Item 2: quantity fixed (setting: allow only 1 item)

When I order the grouped item and select the quantity of item 1 the plugin ends up with counting only item 1 and its quantity.

The idea is to create a bundle where a one items quantity can be selected as item 2 is a one-time-payment with registration (setup fee).

https://wordpress.org/plugins/woocommerce/