Swift 3
I've run into this as well - when you navigate or unwind back to the table view it usually doesn't deselect the previously selected row for you. I put this code in the table view controller & it works well:
override func viewDidAppear(_ animated: Bool) {
if let lastSelectedRow = tableView.indexPathForSelectedRow {
tableView.deselectRow(at: lastSelectedRow, animated: true)
}
}