Reopening a closed milestone from the Closed Milestones page fails

ZD: https://gitlab.zendesk.com/agent/tickets/101358

Clicking Reopen Milestone on the Closed Milestones page throws a HTTP ERROR 400 error. From a personal instance, here's the error in the logs:

2018-08-02T20:43:41.340786761Z ==> /var/log/gitlab/gitlab-rails/production.log <==
2018-08-02T20:43:41.340791356Z
2018-08-02T20:43:41.340794561Z ActionController::ParameterMissing (param is missing or the value is empty: milestone):
2018-08-02T20:43:41.340797173Z   app/controllers/projects/milestones_controller.rb:130:in `milestone_params'
2018-08-02T20:43:41.340799656Z   app/controllers/projects/milestones_controller.rb:63:in `update'
2018-08-02T20:43:41.340802570Z   lib/gitlab/i18n.rb:51:in `with_locale'
2018-08-02T20:43:41.340805902Z   lib/gitlab/i18n.rb:57:in `with_user_locale'
2018-08-02T20:43:41.340808325Z   app/controllers/application_controller.rb:370:in `set_locale'
2018-08-02T20:43:41.340810802Z   lib/gitlab/middleware/multipart.rb:97:in `call'
2018-08-02T20:43:41.340813232Z   lib/gitlab/request_profiler/middleware.rb:14:in `call'
2018-08-02T20:43:41.340815672Z   ee/lib/gitlab/jira/middleware.rb:15:in `call'
2018-08-02T20:43:41.340818635Z   lib/gitlab/middleware/go.rb:17:in `call'
2018-08-02T20:43:41.340821052Z   lib/gitlab/etag_caching/middleware.rb:11:in `call'
2018-08-02T20:43:41.340823608Z   lib/gitlab/middleware/read_only/controller.rb:38:in `call'
2018-08-02T20:43:41.340826729Z   lib/gitlab/middleware/read_only.rb:16:in `call'
2018-08-02T20:43:41.340829145Z   lib/gitlab/request_context.rb:18:in `call'
2018-08-02T20:43:41.340831515Z   lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
2018-08-02T20:43:41.340833997Z   lib/gitlab/middleware/release_env.rb:10:in `call'

My personal instance was running 11.1.4-ee.

Example url on gitlab.com: https://gitlab.com/harish_test_group/push-rules/milestones?sort=due_date_desc&state=closed Click Reopen Milestone to see the error.