How to animate UITableView header view

Question

I need to animate the insertion of a tableview header view. I want that the table rows to slide down while the header view expands its frame.
So far the best result I go

Answer 1

The selected answer didn't work for me. Had to do the following:

[UIView animateWithDuration: 0.5f
                 animations: ^{
                     CGRect frame = self.tableView.tableHeaderView.frame;
                     frame.size.height = self.headerViewController.preferredHeight;
                     self.tableView.tableHeaderView.frame = frame;
                     self.tableView.tableHeaderView = self.tableView.tableHeaderView;
                   }];

The really peculiar part is that this works in one view but not in a subclass of the same view controller / view hierarchy.