title: iOS view controller memory not released after it's been dismissed
body: <p>When the user clicks a button it presents a new tab bar view controller with two view controllers. Here's how I do that</p>
  <pre><code>ACLevelDownloadController *dvc = [[ACLevelDownloadController alloc] initWithNibName:@&quot;ACLevelDownloadController&quot; bundle:[NSBundle mainBundle]];
  ACInstalledLevelsController *ivc = [[ACInstalledLevelsController alloc] initWithNibName:@&quot;ACInstalledLevelsController&quot; bundle:[NSBundle mainBundle]];
  UITabBarController *control = [[UITabBarController alloc] init];
  control.viewControllers = @[dvc, ivc];
  dvc.tabBarItem = [[UITabBarItem alloc] initWithTabBarSystemItem:UITabBarSystemItemFeatured tag:0];
  ivc.tabBarItem = [[UITabBarItem alloc] initWithTabBarSystemItem:UITabBarSystemItemDownloads tag:1];
  [self presentViewController:control animated:YES completion:nil];
  </code></pre>
  <p>this works fine. I dismiss that view controller with a <code>dismiss</code> method in both the <code>ACLevelDownloadController</code> and <code>ACInstalledLevelsController</code>. That also works fine. What's strange is that the memory usage goes up when I present the view controller
  <img src="https://i.stack.imgur.com/nzlQU.png" alt="enter image description here" /></p>
  <p>but it never goes back down. If I present it again, it goes up even more
  <img src="https://i.stack.imgur.com/DBpR4.png" alt="enter image description here" />
  I'm using ARC. Why is the memory that the view controllers use not being released after they are dismissed?</p>
  <h2>EDIT</h2>
  <p>The way they are dismissed is both <code>ACLevelDownloadController</code> and <code>ACInstalledLevelsController</code> have IBActions hooked up that call this method when they are clicked</p>
  <pre><code>- (void)dismiss:(id)sender{
      [self dismissViewControllerAnimated:YES completion:nil];
  }
  </code></pre>