salt-cloud hangs when cloud.providers contains an 'extends' keyword

broken_by_extends_keyword__cloud.providers.d--ec2.conf

# causes salt-cloud to hang

my-aws-ubuntu:
  - id: XXXXXXXX
    ssh_interface: private_ips
    grains:
      node_type: managed
    key: 'XXXXXXXX'
    private_key: /etc/salt/salt-master.pem
    keyname: salt-master
    location: us-east-1
    availability_zone: us-east-1b
    ssh_username: ubuntu
    iam_profile: 'arn:aws:iam::XXXXXXXXXX:instance-profile/salt-minion'
    provider: ec2
    security-group: sg-XXXXXXXX

operations-aws:
  - extends: my-aws-ubuntu

cloud.profiles

ops_docker:
  provider: my-aws-ubuntu    # note that this isn't even the 'operations-aws' provider!
  image: ami-018c9568
  size: m3.medium
  volumes:
    - { size: 10, device: /dev/sdf, type: standard }
  grains:
    roles:
      - docker-host
  tag: { 'roles': 'docker-host' }
  sync_after_install: all
  del_all_vols_on_destroy: True
  script_args: -p python-boto

output of salt-cloud -p ops_docker docker00 -l debug

➜  ~  _ salt-cloud -p ops_docker docker00 -l debug
[DEBUG   ] Reading configuration from /etc/salt/cloud
[DEBUG   ] Reading configuration from /etc/salt/master
[DEBUG   ] Missing configuration file: /etc/salt/cloud.providers
[DEBUG   ] Including configuration from '/etc/salt/cloud.providers.d/ec2.conf'
[DEBUG   ] Reading configuration from /etc/salt/cloud.providers.d/ec2.conf

(...wait a few minutes, nothing happens)

^C
Exiting gracefully on Ctrl-c

working_no_extends_keyword__cloud.providers.d--ec2.conf

# working version

my-aws-ubuntu:
  - id: XXXXXXXXXXXXXXX
    ssh_interface: private_ips
    grains:
      node_type: managed
    key: 'XXXXXXXXXXXXX'
    private_key: /etc/salt/salt-master.pem
    keyname: salt-master
    location: us-east-1
    availability_zone: us-east-1b
    ssh_username: ubuntu
    iam_profile: 'arn:aws:iam::XXXXXXXXXXX:instance-profile/salt-minion'
    provider: ec2
    security-group: sg-XXXXXXXX