Why is the leading swipe action also duplicated as a trailing action?

I have implemented a leading swipe action ('Delete') on my tableView which for a reason I can't figure out is also appearing as a trailing swipe action. See code below:

func tableView(_ tableView: UITableView, leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) ->
    UISwipeActionsConfiguration? {
    let delete1 = deleteAction(at: indexPath)
    return UISwipeActionsConfiguration(actions: [delete1])
}

func deleteAction(at indexPath: IndexPath) -> UIContextualAction {
    let action = UIContextualAction(style: .destructive, title: "Delete") { (action, view, completion) in
        self.delete(at: indexPath)
    }
    return action
}

I used to have a trailing swipe action, but I deleted this function out completely. When I change 'leadingSwipeActionsConfigurationForRowAt' to 'trailingSwipeActions...' then only the trailing swipe action appears. Be grateful if anyone could tell me what I've missed. Thanks.

Use this code to prevent trailingSwipeAction()

    func tableView(_ tableView: UITableView, editingStyleForRowAt indexPath: IndexPath) -> UITableViewCell.EditingStyle
    {
        return .none
    }

• or

    func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
        return UISwipeActionsConfiguration(actions: [])
    }