title: Ember.js 2.0 - modifying property twice in a single render deprecation warning
body: <p>I'm developing a application with the current Ember 2.0 beta release (beta 1), and have started to see this deprecation warning:</p>
  
  <blockquote>
    <p>You modified XXX twice in a single render. This was unreliable in Ember 1.x and will be removed in Ember 2.0</p>
  </blockquote>
  
  <p>It looks like the offenders are computed properties that are being recalculated multiple times because their dependent key(s) are being updated multiple times in a single run loop. However the stack traces for the deprecations don't lead back to any of my application code, and I thought this was something Ember should already be silently taking care of for me anyway.</p>
  
  <p>Is this something I need to actively fix in my app code before updating to v2.0 final when its released, or is it just more of an 'internal' deprecation notice? If I do need to make changes, is there any common anti-patterns or gotchas I should look out for that would cause this error?</p>