title: UIKeyboard notification handler triggered 3 times
body: <p>My code:</p>
  
  <pre><code>-(void)viewWillAppear:(BOOL)animated {
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleKeyboard:) name:UIKeyboardWillChangeFrameNotification object:nil];
  }
  
  -(void)viewWillDisappear:(BOOL)animated {
      [[NSNotificationCenter defaultCenter] removeObserver:self];
  }
  
  -(void)handleKeyboard:(NSNotification*)notification {
    NSLog(@"triggered");
  }
  </code></pre>
  
  <p>See:</p>
  
  <p><img src="https://i.stack.imgur.com/Xa3Ji.gif" alt="enter image description here"></p>
  
  <p>The disappearing handler is triggered once as normal, but 3 times when appears. Is this a iOS bug?</p>