Grape on reel-rack return nothing when "Connection: close" header received

[a0s]

I have test server

require 'grape'

class APIv2 < Grape::API
  format :json
  default_format :json

  get :test do
    puts 'request!'
    {:result => 'OK'}
  end
end

run APIv2

bundle exec reel-rack test_server.ru

Testing it with curl

$ curl "http://localhost:3000/test" -H "Connection: close"
curl: (18) transfer closed with outstanding read data remaining
$ curl "http://localhost:3000/test"
{"result":"OK"}