activeadmin: broken has_many form

Hello)

Recently, I used has_many form and encountered with problem: how can I distinguish has_many objects during editing?

the simple ways were to use labeled inputs block, like:

ActiveAdmin.register Pricelist do
  permit_params :name, :description, prices_attributes: [:amount]

  form do |f|
    # ......
    f.has_many :prices, heading: false, allow_destroy: false, new_record: false do |price|
       price.inputs "#{price.object.try!(:city).try!(:name)}" do
         price.input :amount
      end
    end
    # ....
  end

or panels:

form do |f|
  # ......
  f.has_many :prices, heading: false, allow_destroy: false, new_record: false do |price|
     panel "#{price.object.try!(:city).try!(:name)}" do
       price.input :amount
    end
  end
  # ....
end

but i found that every time form was broken the best temporary solution was wrapping has_many records in main form inputs block:

form do |f|
  # ......
  f.has_many :prices, heading: false, allow_destroy: false, new_record: false do |price|
     price.inputs "#{price.object.try!(:city).try!(:name)}" do
       f.input :amount
    end
  end
  # ....
end

it still was broken but looks not so bad (except empty space in form end that get bigger cause there are hidden id inputs)

I create simple test project) and add branch that recreates this problem branch: broken_has_many_form

Can someone help me to solve this problem?)