I recently upgraded to Foreman 1.5.0 and just discovered that I can't provision a new VM when the initial attempt results in any DNS issue.  I get a 500 response stating that the MAC address is invalid.

I get the following stack trace in the GUI:

Net::Validations::Error
Invalid MAC 
lib/net/validations.rb:19:in `validate_mac'
lib/net/dhcp/record.rb:7:in `initialize'
app/models/concerns/orchestration/dhcp.rb:16:in `new'
app/models/concerns/orchestration/dhcp.rb:16:in `dhcp_record'
app/models/concerns/orchestration/dhcp.rb:120:in `queue_remove_dhcp_conflicts'
app/models/concerns/orchestration/dhcp.rb:73:in `queue_dhcp'
app/models/concerns/orchestration.rb:47:in `valid?'
app/models/concerns/foreman/sti.rb:29:in `save_with_type'
app/controllers/hosts_controller.rb:94:in `create'
app/models/concerns/foreman/thread_session.rb:33:in `clear_thread'
lib/middleware/catch_json_parse_errors.rb:9:in `call'

From Foreman's production log:

Started POST "/hosts" for 10.103.100.234 at 2014-05-21 13:57:42 -0400
Processing by HostsController#create as */*
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"LFrxz49nB00DpkYELn2TOJiIv6Z9TSL8vye7YQXKrns=", "host"=>{"name"=>"rabbitmq-bulk-1", "hostgroup_id"=>"3", "compute_resource_id"=>"1", "compute_profile_id"=>"8", "environment_id"=>"6", "puppet_ca_proxy_id"=>"1", "puppet_proxy_id"=>"1", "puppetclass_ids"=>["", "29"], "managed"=>"true", "progress_report_id"=>"[FILTERED]", "type"=>"Host::Managed", "compute_attributes"=>{"cpus"=>"4", "corespersocket"=>"1", "memory_mb"=>"4096", "cluster"=>"Dell R620", "path"=>"/Datacenters/NJ3/vm", "guest_id"=>"centos64Guest", "interfaces_attributes"=>{"new_interfaces"=>{"type"=>"VirtualE1000", "network"=>"network-1024", "_delete"=>""}, "0"=>{"type"=>"VirtualE1000", "network"=>"network-1024", "_delete"=>""}}, "volumes_attributes"=>{"new_volumes"=>{"datastore"=>"depot03", "name"=>"Hard disk", "size_gb"=>"10", "thin"=>"true", "_delete"=>""}, "0"=>{"datastore"=>"depot03", "name"=>"Hard disk", "size_gb"=>"10", "thin"=>"true", "_delete"=>""}}, "scsi_controller_type"=>"VirtualLsiLogicController", "start"=>"1"}, "domain_id"=>"2", "realm_id"=>"", "mac"=>"", "subnet_id"=>"3", "ip"=>"192.168.0.75", "interfaces_attributes"=>{"new_interfaces"=>{"_destroy"=>"false", "type"=>"Nic::Managed", "mac"=>"", "name"=>"", "domain_id"=>"", "ip"=>"", "provider"=>"IPMI"}}, "architecture_id"=>"1", "operatingsystem_id"=>"4", "provision_method"=>"build", "build"=>"1", "medium_id"=>"1", "ptable_id"=>"18", "disk"=>"", "root_pass"=>"[FILTERED]", "is_owned_by"=>"2-Users", "enabled"=>"1", "comment"=>"", "overwrite"=>"true"}, "capabilities"=>"build image", "provider"=>"Vmware"}
Operation FAILED: Invalid MAC
  Rendered common/500.html.erb (4.6ms)
Completed 500 Internal Server Error in 233ms (Views: 6.9ms | ActiveRecord: 4.1ms)

There is absolutely nothing in the foreman proxy log.

To clarify, this occurs when attempting to provision a new machine on VMware.  The auto-suggested IP was previously in use, so a PTR record already exists. I ack the warning and click "Overwrite" and then get the 500 error.