Cloning a hostgroup fails when it contains at least one parameter

Environment:
- CentOS 7
- Foreman 1.8.2
- postgresql 9.2.13

- Fresh install of Foreman
- Freshly created hostgroup named Default
- Clone hostgroup to Test1 (no parameters added) renders success
- Add a parameter (parameter_test=>Testvalue) and save renders success
- Clone the hostgroup to Test1 redirects to https://<foremanhost>/hostgroups without actually cloning the hostgroup.

Excerpt from production.log:

Started POST "/hostgroups" for aa.bb.cc.dd at 2015-07-27 12:01:33 +0200
2015-07-27 12:01:33 [I] Processing by HostgroupsController#create as HTML
2015-07-27 12:01:33 [I] Parameters: {"utf8"=>"✓", "authenticity_token"=>"wInPQcIAaP8AbUQHoTCWhCF1RvA+xtQI4Q1FMZZM3RY=", "hostgroup"=>{"parent_id"=>"", "name"=>"Test1", "environment_id"=>"2", "puppet_ca_proxy_id"=>"1", "puppet_proxy_id"=>"1", "puppetclass_ids"=>[""], "domain_id"=>"", "realm_id"=>"", "architecture_id"=>"", "root_pass"=>"[FILTERED]", "group_parameters_attributes"=>{"0"=>{"name"=>"parameter_test", "value"=>"[FILTERED]", "hidden_value"=>"[FILTERED]", "_destroy"=>"false", "nested"=>"", "id"=>"41"}}, "id"=>""}, "commit"=>"Submit"}
2015-07-27 12:01:33 [I] Rendered common/404.html.erb within layouts/application (0.9ms)
2015-07-27 12:01:33 [I] Rendered layouts/base.html.erb (1.7ms)
2015-07-27 12:01:33 [I] Completed 404 Not Found in 15ms (Views: 4.5ms | ActiveRecord: 1.2ms)