Black bar over a TableView just above TabBar

I have a UITableView with cells which perform a segue to an other simple detail view. The UITableView and detail view are embed in a Navigation Controller.

On my UITableView I put a UISearchController bar folowing this tutorial: http://ift.tt/1dStQBT

So now, I have the following graphic problem: When I perform a segue by tapping a cell after having make a research, I arrive to my detail view. But when I tap the Back button in the Navigation Bar, a mysterious black bar appears just above the TabBar. When the animation is over, the black bar disappears.

But when I tap the return button from the detail view without having done a research to arrive at this detail view, there is no black bar.

I can't understand why there is that black bar. I just note the black bar's height is equal to the TabBar's height. Maybe a link ?