1. Open up the Subnets index page
2. Open up the New Host form in a separate tab
3. Select a subnet in the New Host form with IP suggestions, which should populate
4. Select a subnet to edit on the Subnet index
5. Save the subnet

It will redirect the two pane page to /hosts/new, so you end up with an embedded New Host form in the pane (see screenshot).

2015-08-06T08:51:51 [app] [I] Started PUT "/subnets/7-libvirt%203" for 127.0.0.1 at 2015-08-06 08:51:51 +0100
2015-08-06T08:51:51 [app] [I] Processing by SubnetsController#update as */*
2015-08-06T08:51:51 [app] [I]   Parameters: {"utf8"=>"✓", "authenticity_token"=>"rO7+DbD+3h1/Pk5qZ2s+L4bmY6a80mzRHXgU7YDsJGA=", "subnet"=>{"name"=>"libvirt 3", "network"=>"192.168.122.0", "mask"=>"255.255.255.0", "gateway"=>"192.168.122.1", "dns_primary"=>"192.168.122.1",
 "dns_secondary"=>"", "ipam"=>"DHCP", "from"=>"", "to"=>"", "vlanid"=>"", "boot_mode"=>"DHCP", "domain_ids"=>[""], "dhcp_id"=>"", "tftp_id"=>"", "dns_id"=>""}, "redirect"=>"", "id"=>"7-libvirt 3"}
...
2015-08-06T08:51:51 [app] [I] Redirected to http://0.0.0.0:3000/hosts/new
2015-08-06T08:51:51 [app] [I] Completed 302 Found in 17.7ms (ActiveRecord: 1.1ms)

What appears to be happening is that the AJAX request on the New Host form hits the subnet controller, which triggers the store_redirect_to_url filter in app/controllers/concerns/foreman/controller/auto_complete_search.rb. The filter should probably only store the URL if !ajax?.

This might happen with other controllers, such as images which is used for CRs in the New Host form.