title: UIScrollView not scrolling when set to a tableView's tableHeaderView
body: <p>I'm having difficulty scrolling a UIScrollView instance in my UITableView when I set it as a tableHeaderView. </p>
  
  <p>It still responds to touch events it appears, but doesn't wish to scroll horizontally. I've tried explicitly setting to setUserInteractionEnabled:YES without much luck.</p>
  
  <p>Is there something in particular I need to do to get scrolling working when this is set as a tableHeaderView?</p>
  
  <p>Thanks.</p>