In the production log, it looks like it's not even taking the parameters specified in the web interface from the POST:
Started PUT "/compute_profiles/5-web-server/compute_attributes/2" for 10.30.39.50 at 2014-05-12 09:25:08 -0500
Processing by ComputeAttributesController#update as */*
Parameters: {"utf8"=>"✓", "authenticity_token"=>"xxx/k=", "compute_attribute"=>{"vm_attrs"=>{"cpus"=>"1", "corespersocket"=>"2", "memory_mb"=>"1024", "cluster"=>"LAN", "path"=>"/Web Developers", "guest_id"=>"centos64Guest", "interfaces_attributes"=>{"new_interfaces"=>{"type"=>"VirtualE1000", "network"=>"dvportgroup-526", "_delete"=>""}, "0"=>{"type"=>"VirtualVmxnet3", "network"=>"dvportgroup-530", "_delete"=>""}}, "volumes_attributes"=>{"new_volumes"=>{"datastore"=>"wrongdatastore", "name"=>"Hard disk", "size_gb"=>"10", "thin"=>"true", "_delete"=>""}, "0"=>{"datastore"=>"rightdatastore", "name"=>"Hard disk", "size_gb"=>"10", "thin"=>"true", "_delete"=>""}}, "scsi_controller_type"=>"VirtualLsiLogicController"}}, "compute_profile_id"=>"5-web-server", "id"=>"2"}
Successfully decrypted field for Foreman::Model::Vmware VMware
Redirected to https://ddpuppet/compute_profiles/5-web-server
Completed 302 Found in 292ms (ActiveRecord: 3.8ms)