title: Why "m2m_changed" signals never gets fired from the admin site?
body: <p>Well, dont know if this is a bug or if I've a concept error. But try to test it:</p>
  
  <p>A simple generic test:</p>
  
  <pre><code>from django.dispatch import receiver
  from django.db.models.signals import m2m_changed
  
  @receiver(m2m_changed)
  def test_handler(sender, instance, action, reverse, model, pk_set, **kwargs):
       import sys
       print&gt;&gt;sys.stderr, action
  </code></pre>
  
  <p>Add this snippet to your code and try to edit a model from the admin that contains a m2m relation. You can add or delete an object to the relationship. Then, you will see that the signal doesn't fire: S</p>
  
  <p>Instead, if you do the same from a shell ... everything works fine.</p>
  
  <p>Could anyone try it and confirm it is not a paranormal activity at my computer?</p>
  
  <p>Thanks in advance.</p>