Search string break when searching

I don't know why, but I get a break between the search bar and the results, as if the area buttons were showing, only they are not.

In the image, the highlighted view is UISearchBarContainerView and the border view is UITableViewWrapperView

Image: http://blog.minetheapp.com/wp-content/uploads/searchgap.jpg

Here's the code to create the search bar:

// set up results controller
let resultsController = SearchResultsController()
searchController = UISearchController(searchResultsController: resultsController)

// set up search bar in article table
let searchBar = searchController.searchBar
searchBar.placeholder = "Procurar Artigo"
searchBar.sizeToFit()

articleTable.tableHeaderView = searchBar
searchController.searchResultsUpdater = resultsController