title: Imagekit - cache image not deleted after deleting original
body: <p>In my project I have a model where I use Imagekit to process an image. When I save an image I have following requirements:</p>
  
  <ul>
  <li>rename image and thumbnail to a unique name</li>
  <li>when a new image is loaded, the old one should be removed (and the thumbnail in the cache should refresh to the new image).</li>
  </ul>
  
  <p>To accomplish this, I use following code:</p>
  
  <p>The model:</p>
  
  <pre><code>def generate_cache_filename(instance, path, specname, extension):
      extension = '.jpg'
      return 'cache/images_upload/%s_%s%s' % (instance.pk, specname, extension)
  
  def generate_image_filename_1(instance, filename):
      filename = '1'
      extension = '.jpg'
      return 'images_upload/%s_%s%s' % (instance.pk, filename, extension)
  
  class Model(models.Model):
      name = models.CharField(max_length=40)
      image_1 = ProcessedImageField([Adjust(contrast=1.2, sharpness=1.1), ResizeToFill(500, 370)], upload_to=generate_image_filename_1, format='JPEG', options={'quality': 90})
      thumbnail_1 = ImageSpec([Adjust(contrast=1.2, sharpness=1.1), ResizeToFill(83, 78)], image_field='image_1', cache_to=generate_cache_filename, format='JPEG', options={'quality': 90})
  </code></pre>
  
  <p>The form (to delete the image when it is replaced by a new one):</p>
  
  <pre><code>if form.is_valid():
      form_image = form.cleaned_data['image_1']
          try:
              details = Model.objects.get(pk=pk)
              if details.image_1 != form_image:
                  details.image_1.delete(save=False)
          except Model.DoesNotExist: 
              pass
          form.save()
  </code></pre>
  
  <p>The part of renaming the images and replacing <code>image_1</code> (= loading new and deleting old) works just fine. But for some reason the <code>thumbnail_1</code> in the cache does not refresh (= is still the thumbnail of the old image).  </p>
  
  <p>I think it has something to do with the deletion code in the form, but I can't figure out why and how to solve it. Someone with suggestions?</p>
  
  <p><strong>UPDATE 1</strong>: it has also something to do with the 'renaming'. I did some extra tests: when I don't rename the <code>image_1</code> file, then everything works fine (also refreshing of the thumbnail). But when I load another image with the same name, then I have the same problem: <code>image_1</code> is updated, but <code>thumbnail_1</code> is still the thumbnail of the old image.</p>
  
  <p><strong>UPDATE 2</strong>: did some more tests and when uploading a new image with the same filename, I definitely enter the <code>if statement</code> in <code>try</code>. So the old image is deleted. According to the documentation of Imagekit, the thumbnail should also be deleted. But this is not the case. </p>
  
  <p>Many thanks!</p>