title: buggy margin behavior with dynamically resizing UITextView
body: <p>I need a dynamically resizing UITextView but the right margin encroaches towards the left alarmingly after numerous resizes so that a very narrow strip of text is shown with lots of white space in the text view. This can be reproduced by a simple setup with just a UITextView and UISlider. A simple sample setup that produces this behavior is UISlider with value range from 0-200, a UITextView of 320 width and this code:</p>
  
  <pre><code>- (IBAction)sliderValueChanged:(UISlider *)slider {
      textView.frame = CGRectMake(0, 0, 320 - slider.value, 300);
  }
  </code></pre>
  
  <p>Some things I've tried are tinkering with the autoResizingMask, contentMode, contentOffset, and sizeToFit but none of them work. How can this weird behavior be avoided, or is it a bug?</p>