title: Strange occurance when editing model attribute
body: <p>My Models look like this:</p>
  
  <pre><code>class Model1(models.Model):
    ...
  
  class Model2(models.Model):
      model1 = models.ForeignKey(Model1)
      attr = models.IntegerField(default=1)
  </code></pre>
  
  <p>From the shell, I see the following behavior:</p>
  
  <pre><code>&gt;&gt;&gt; m1.model2_set.all()[0].attr += 1
  &gt;&gt;&gt; m1.model2_set.all()[0].attr
  1
  &gt;&gt;&gt; m2 = m1.model2_set.all()[0]
  &gt;&gt;&gt; m2.attr += 1
  2
  </code></pre>
  
  <p>Any idea why this would happen?</p>