Trying to use busybox in a snap results in errors

[Jamie Bennett]

Adding busybox to a snap with the following yaml triggers an error on snapcraft 2.9.
Yaml:

name: taskwarrior-jamiebennett
version: 2.5.1
summary: Taskwarrior manages your TODO list from the command line.
description: Taskwarrior is Free and Open Source Software that manages your TODO list from the command line. It is flexible, fast, and ubobtrusive. It does its job then gets out of your way.
confinement: devmode # use "strict" to enforce system access only via declared interfaces

build-packages: [libc6, libgcc1, libgnutls-dev, libstdc++6, uuid-dev]

apps:
  taskwarrior:
    command: task
  busybox:
    command: sh
parts:
  taskwarrior:
    plugin: cmake
    make-parameters:
      - -DCMAKE_BUILD_TYPE=release .
    source: https://taskwarrior.org/download/task-2.5.1.tar.gz
  busybox:
    plugin: nil
    stage-packages:
      - busybox

Error:
jtar: Exiting with failure status due to previous errors
dpkg-deb: error: subprocess tar returned error exit status 2
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/snapcraft/internal/repo.py", line 179, in unpack
    subprocess.check_call(['dpkg-deb', '--extract', pkg, rootdir])
  File "/usr/lib/python3.5/subprocess.py", line 581, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['dpkg-deb', '--extract', '/media/jamie/UNTITLED/development/snaps/taskwarrior/parts/busybox/ubuntu/download/gcc-6-base_6.0.1-0ubuntu1_amd64.deb', '/media/jamie/UNTITLED/development/snaps/taskwarrior/parts/busybox/install']' returned non-zero exit status 2

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/snapcraft", line 31, in <module>
    snapcraft.main.main()
  File "/usr/lib/python3/dist-packages/snapcraft/main.py", line 146, in main
    return run(args, project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/main.py", line 193, in run
    lifecycle.snap(project_options, args['<directory>'], args['--output'])
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 242, in snap
    snap = execute('strip', project_options)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 84, in execute
    _Executor(config, project_options).run(step, part_names)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 113, in run
    self._run_step(step, part, part_names, dirty, recursed)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/lifecycle.py", line 148, in _run_step
    getattr(part, 'prepare_{}'.format(step))()
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 264, in prepare_pull
    self._unpack_stage_packages()
  File "/usr/lib/python3/dist-packages/snapcraft/internal/pluginhandler.py", line 258, in _unpack_stage_packages
    self.ubuntu.unpack(self.installdir)
  File "/usr/lib/python3/dist-packages/snapcraft/internal/repo.py", line 181, in unpack
    raise UnpackError(pkg)
snapcraft.internal.repo.UnpackError: /media/jamie/UNTITLED/development/snaps/taskwarrior/parts/busybox/ubuntu/download/gcc-6-base_6.0.1-0ubuntu1_amd64.deb