interactive keyboard dismiss bug

DetailViewController.swift

import UIKit

class DetailViewController: UIViewController {
    
    @IBOutlet weak var scrollView: UIScrollView!
    
    var textView: UITextView?
    var detailItem: AnyObject?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardDidShow:", name: UIKeyboardDidShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillHide:", name: UIKeyboardWillHideNotification, object: nil)
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        if let scrollView = scrollView {
            textView = UITextView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
            
            let content = "fj fdslkf jfsdl kfjsdfl ksjfsdlkjf s " +
                "flkf jsf sdlf jdsflksdj flskj flsdkfj k" +
                "lfds jflsdkfj lsdfj flkdsjf lskdfj slkjfd sdlfk" +
                "flkf jsf sdlf jdsflksdj flskj flsdkfj k" +
                "lfds jflsdkfj lsdfj flkdsjf lskdfj slkjfd sdlfk" +
                "flkf jsf sdlf jdsflksdj flskj flsdkfj k"
            
            textView?.text = content
            
            scrollView.addSubview(textView!)
            
            var newScrollViewContentSize = CGSize(width: textView!.frame.width, height: textView!.frame.height)
            scrollView.contentSize = newScrollViewContentSize
            
            var newInsets = UIEdgeInsets(top: topLayoutGuide.length, left: 0, bottom: 0, right: 0)
            scrollView.contentInset = newInsets
            scrollView.scrollIndicatorInsets = newInsets
        }
    }
    
    func keyboardDidShow(notification: NSNotification) {
        println("did show")
        
        if let scrollView = scrollView {
            let info: NSDictionary = notification.userInfo!
            let kbSize = info.objectForKey(UIKeyboardFrameEndUserInfoKey)!.CGRectValue().size
            var newInsets = UIEdgeInsets(top: topLayoutGuide.length, left: 0, bottom: kbSize.height, right: 0)
            scrollView.contentInset = newInsets
            scrollView.scrollIndicatorInsets = newInsets
        }
    }
    
    func keyboardWillHide(notification: NSNotification) {
        println("will hide")
        
        if let scrollView = scrollView {
            var newInsets = UIEdgeInsets(top: topLayoutGuide.length, left: 0, bottom: 0, right: 0)
            scrollView.contentInset = newInsets
            scrollView.scrollIndicatorInsets = newInsets
        }
    }
    
}