Prevent table section header views from sticking at the top of the table view

gistfile1.m

// Implement this in the UITableView's subclass
// Please note that you have to return an instance of UITableViewHeaderFooterView's subclass in tableView:viewForHeaderInSection:
// 

- (void)layoutSubviews {
  [super layoutSubviews];
  NSArray *visibleRows = [self indexPathsForVisibleRows];
  NSMutableIndexSet *sections = [[NSMutableIndexSet alloc] init];
  for (NSIndexPath *indexPath in visibleRows) {
    [sections addIndex:indexPath.section];
  }
  [sections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
    UIView *headerView = [self headerViewForSection:idx];
    CGRect headerFrame = headerView.frame;
    NSIndexPath *firstRow = [NSIndexPath indexPathForRow:0 inSection:idx];
    CGRect firstRowFrame = [self rectForRowAtIndexPath:firstRow];
    headerFrame.origin.y = firstRowFrame.origin.y - headerFrame.size.height;
    headerView.frame = headerFrame;
  }];
}