title: STATICFILES_DIRS setting makes my admin widget override disappear
body: <p>I'm having trouble understanding how static files are handled in Django. I've read through the official Django documentation as well as multiple threads, including this wonderful one here:</p>
  
  <p><a href="https://stackoverflow.com/questions/24022558/differences-between-staticfiles-dir-static-root-and-media-root">Differences between STATICFILES_DIR, STATIC_ROOT and MEDIA_ROOT</a></p>
  
  <p>Most people define the STATICFILES_DIRS list as a list of paths where django will search for additional static files aside from the app's static folder.</p>
  
  <p>I understand that, but what does this have to do with the formfields I'm overriding in my admin.py?
  I have overridden the default ManyToMany form to the FilteredSelectMultiple widget in a few of my admin models like so:</p>
  
  <pre><code>from django.contrib.admin.widgets import FilteredSelectMultiple
  
  formfield_overrides = {
      models.ManyToManyField: {'widget': FilteredSelectMultiple("User Names", is_stacked=False)}
  }
  </code></pre>
  
  <p>This works fine and produces the widget override I wanted: <a href="https://i.stack.imgur.com/SI2e7.png" rel="nofollow noreferrer">Functional Widget Screenshot</a></p>
  
  <p>However, when I define STATICFILES_DIRS in settings.py to include my root static folder like so:</p>
  
  <pre><code>STATICFILES_DIRS = (
      os.path.join(BASE_DIR, 'static/'),
  )
  </code></pre>
  
  <p>It breaks my override and defaults back to the original ManyToMany field form:
  <a href="https://i.stack.imgur.com/I0BkV.png" rel="nofollow noreferrer">Broken Widget Screenshot</a></p>
  
  <p>We do not have STATIC_ROOT defined in our settings.py as we don't plan on using the collect static feature. We plan on keeping/referencing our static files at the root static folder. Also in our settings.py we have:</p>
  
  <pre><code>STATIC_URL = '/static/'
  </code></pre>
  
  <p>I don't understand how these settings for dealing with static files are interfering with the formfield_override above. I would appreciate some insight on this, so that I could find a way to approach this issue.</p>
  
  <p>Thank you!</p>