title: NSDateFormatter error, return date one year ago
body: <p>Code:</p>
  
  <pre><code>NSString *ds = @"2013-02-25";
  NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
  [formatter setDateFormat:@"YYYY-MM-dd"];
  NSDate* date = [formatter dateFromString:ds];
  NSLog(@"%@", date); //2012-02-24 16:00:00 +0000
  [formatter setDateFormat:@"MMM dd, YYYY"];
  NSLog(@"%@", [formatter stringFromDate:date]); //Feb 25, 2012
  </code></pre>
  
  <p>Is there something wrong I made? Or iOS 6 SDK bug?</p>