packer fast path bug

packer.json

{
    "variables": {},
    "provisioners": [
      {
        "type": "file",
        "source": "minimal.json",
        "destination": "/tmp/minimal.json"
      }
    ],
    "builders": [
      {
        "type": "googlecompute",
        "account_file": "{{user `account_file`}}",
        "project_id": "{{user `project_id`}}",
        "image_name": "packerbats-scp-{{timestamp}}",
        "source_image": "debian-7-wheezy-v20141108",
        "zone": "us-central1-a"
      }
    ]
}