2018-04-08T10:16:14 [I|app|] Started PATCH "/subnets/1" for 10.35.2.157 at 2018-04-08 10:16:14 +0100
2018-04-08T10:16:14 [I|app|bcb27] Processing by SubnetsController#update as */*
2018-04-08T10:16:14 [I|app|bcb27]   Parameters: {"utf8"=>"✓", "authenticity_token"=>"9qAyRmK8xfdqNQZfkEhoSxP2IDqD1K83SyAL3lpcxRMQaq3+O4+UK2ou9Bsi0wrg0F0xP/5YJLscQI1aYD+Wbw==", "subnet"=>{"name"=>"SAT Lab 180", "description"=>"", "network"=>"10.35.27.0", "cidr"=>"26", "mask"=>"255.255.255.192", "gateway"=>"10.35.27.62", "dns_primary"=>"10.35.27.1", "dns_secondary"=>"10.35.255.6", "ipam"=>"DHCP", "from"=>"10.35.27.5", "to"=>"10.35.27.59", "vlanid"=>"180", "mtu"=>"1500", "boot_mode"=>"DHCP", "domain_ids"=>["", "6"], "dhcp_id"=>"5", "tftp_id"=>"1", "dns_id"=>"1", "template_id"=>"", "remote_execution_proxy_ids"=>[""], "location_ids"=>["3", ""], "organization_ids"=>["1", "", "9"]}, "redirect"=>"", "_ie_support"=>"", "id"=>"1"}
2018-04-08T10:16:14 [I|app|bcb27] Current user: admin (administrator)
2018-04-08T10:16:14 [E|app|bcb27] Failed to save: Subnet domains is invalid
2018-04-08T10:16:14 [I|app|bcb27]   Rendering subnets/edit.html.erb

while the UI does not show any error.