When creating a new host, select a libvirt compute resource as the first action and the Virtual Machine tab will fail to load:

NoMethodError - undefined method `[]' for nil:NilClass:
  app/views/compute_resources_vms/form/_libvirt.html.erb:30:in `_app_views_compute_resources_vms_form__libvirt_html_erb__1886783418346172016_70035848515480'
  actionpack (3.2.13) lib/action_view/template.rb:145:in `block in render'

If you select an EC2 CR first, the compute_attributes params get loaded and then loading the libvirt pane works.