Why dismissing view controller is not clearing presented controller from memory?

I have 2 controllers. Each of them have only one button on screen. For first controller button is presenting modally second controller, and for second controller button is dismissing presented controller.

Code of first one is simple as door:

class ViewController: UIViewController {
    @IBAction func present(sender: AnyObject) {
        let storyboard = UIStoryboard(name: "Main", bundle: NSBundle.mainBundle())
        if let controller = storyboard.instantiateViewControllerWithIdentifier("web") as? UIViewController {
            controller.modalTransitionStyle = UIModalTransitionStyle.FlipHorizontal
            self.presentViewController(controller, animated: true, completion: nil)
        }
    }
}

Second controller code contain some extra code for detecting that after dismissing controller still exist.

static var index: Int = 0
var index: Int

required init(coder aDecoder: NSCoder) {
    self.index = WebViewController.index++
    super.init(coder: aDecoder)
    let timer = NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: "action", userInfo: nil, repeats: true)
}

func action() {
    NSLog("Class \(self.dynamicType) index is \(self.index)")
}

And all code of second controller looks like:

class WebViewController: UIViewController {
    static var index: Int = 0
    var index: Int

    required init(coder aDecoder: NSCoder) {
        self.index = WebViewController.index++
        super.init(coder: aDecoder)
        let timer = NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: "action", userInfo: nil, repeats: true)
    }

    func action() {
        NSLog("Class \(self.view) index is \(self.index)")
    }

    @IBAction func dismissSelf() {
        if let presentingController = self.presentingViewController {
            presentingController.dismissViewControllerAnimated(true, completion: nil)
        }
    }
}

So when you will run this and press button on first controller screen for first time, then each 5 seconds you will see in console something like:

Class Proj.WebViewController index is 0

But if you will dismiss controller and present is again, then you will see both:

Class Proj.WebViewController index is 0

Class Proj.WebViewController index is 1

As I understand dismissing is not removing from memory presented controller even if nobody is catching him from my side.

Do somebody know what is it and how can i solve it?

Also you can download sample project