title: Problems animating UIView alpha
body: <p>I'm trying to apply a fade to an UIView I created programmatically on the top of another.</p>
  
  <pre><code>[UIView animateWithDuration:0.5 animations:^(void) {
      [self.view setAlpha:0];
  }
                   completion:^(BOOL finished){
                       [self.view removeFromSuperview];
                   }];
  </code></pre>
  
  <p>The finished event is called properly after exactly 0.5 seconds, but I don't see any fade (I should see the UIView on the bottom).</p>
  
  <p>If instead of using the alpha, I move away the UIView it works (I see the bottom UIView while the top UIView slides away), so it seems to be a problem related to alpha, but I can't figure out what's wrong!</p>
  
  <pre><code>[UIView animateWithDuration:0.5 animations:^(void) {
      CGRect o = self.view.frame;
      o.origin.x = 320;
      self.view.frame = o;
  }
                   completion:^(BOOL finished){
                       [self.view removeFromSuperview];
                   }];
  </code></pre>
  
  <p>I used alpha animations previously and they works in this way usually...</p>