title: UITableView reloadSections/reloadData: header view becomes blank
body: <p>I have a UITableView with some sections, each has its own header view. 
  When user taps on the header view of a section, all rows of that section will collapse. What i do is, I set the number of row of that section to 0, and then call :</p>
  
  <pre><code>[self.tableView reloadSections:sections withRowAnimation:UITableViewRowAnimationBottom];
  </code></pre>
  
  <p>Everything works as expected, except one thing : the header view of the section becomes white blank. When i scroll the table, then the header becomes normal again.</p>
  
  <p>So i guess there's some problem with the drawing of the table. </p>
  
  <p>One funny thing is, if i use UITableViewRowAnimationFade instead, then even when i scroll the table, the header is still white blank.</p>
  
  <p>When I update just ONE section there is also no problem - when I update more than one section the problem occurs.</p>
  
  <p>If i use</p>
  
  <pre><code>[self.tableView reloadData]
  </code></pre>
  
  <p>instead, then everything works fine.</p>
  
  <p>The reason i use </p>
  
  <pre><code>[self.tableView reloadSections:sections withRowAnimation:UITableViewRowAnimationBottom];
  </code></pre>
  
  <p>is because i want animation.</p>
  
  <p>Wrapping with beginUpdates / endupdates does not work.</p>