django model admin fields option has incorrect html view

[Artur Ivanov]

Hello. I've just updated django from 2.0 to 2.1.3 release and I have a problem with django admin site since.
The problem is incorrect html view of model admin fields option.

I have this code in my admin.py

@admin.register(Orders)
class OrdersAdmin(admin.ModelAdmin):
    list_display = ('customer', 'contact_pers', 'get_email',
                    'order_number', 'order_date', 'products_list',
                    'is_add_lic', 'contractor', 'partner')
    fields = ('customer', ('order_number', 'order_date'), 'payment_day',
              'products', 'contact_pers', 'contractor', 'is_add_lic',
              'partner')

According to documentation fields order_number" and "order_date" must be on the same line because they're wraped in their own tuple. Вut it's broke since 2.1.0 release, as I guess.

To demostrate what I actually have I attached a couple of screnshots