Windows error when re-applying users: "if shell and lusr['shell'] != shell"

[jpsv]

Salt-Master (salt 2017.7.4 (Nitrogen)) on Debian 9.3.0 netinstall VM.
Salt-Minion (salt 2017.7.4 (Nitrogen)) (just upgraded from 2017.7.2) on Windows 10 (version 1709 build 16289.248) default install on Dell XPS 13

   ----------
          ID: users_firstname.lastname_user
    Function: user.present
        Name: firstname.lastname
      Result: False
     Comment: An exception occurred in this state: Traceback (most recent call last):
                File "c:\salt\bin\lib\site-packages\salt\state.py", line 1843, in call
                  **cdata['kwargs'])
                File "c:\salt\bin\lib\site-packages\salt\loader.py", line 1795, in wrapper
                  return f(*args, **kwargs)
                File "c:\salt\bin\lib\site-packages\salt\states\user.py", line 485, in present
                  win_description)
                File "c:\salt\bin\lib\site-packages\salt\states\user.py", line 126, in _changes
                  if shell and lusr['shell'] != shell:
              KeyError: 'shell'
     Started: 09:48:29.202000
    Duration: 16.0 ms
     Changes:
    ----------
          ID: users_firstname.lastname_user
    Function: file.directory
        Name: /home/firstname.lastname
      Result: False
     Comment: One or more requisite failed: users.users_firstname.lastname_user
     Changes:

On the Minion, I observe in the Salt Minion debug logs that the system is trying to find a registry key that doesn't exist, a sequentially increasing 4-digit number for the Windows SID. My Pillar (Same error if Shell is omitted or defined as /bin/sh):

users:
  ## Minimal required pillar values
# auser:
#   fullname: A User

  ## Full list of pillar values
  firstname.lastname:
    fullname: Firsty Lasterson
    password: plaintestbullshit
    enforce_password: True
    # WARNING: If 'empty_password' is set to True, the 'password' statement
    # will be ignored by enabling password-less login for the user.
    empty_password: False
    hash_password: False
    prime_group:
      name: Administrators
    shell: ComSpec


    user_files:
      enabled: True
      # 'source' allows you to define an arbitrary directory to sync, useful to use for default files.
      # should be a salt fileserver path either with or without 'salt://'
      # if not present, it defaults to 'salt://users/files/user/<username>
      source: users/files/default
      template: jinja
      # You can specify octal mode for files and symlinks that will be copied. Since version 2016.11.0
      # it's possible to use 'keep' for file_mode, to preserve file original mode, thus you can save
      # execution bit for example.
      file_mode: keep
      sym_mode: 640