iOS. UITextView. Text jumping after UIKeyboardDidHideNotification

I have editable UITextView and keyboard dismiss mode is interactive. Also my controller is listening two notifications: UIKeyboardWillShowNotification, UIKeyboardWillHideNotification.

func keyboardWillShow(notification: NSNotification) {


    if let userInfo = notification.userInfo {

            var insets = self.textView.contentInset;
            let rect = userInfo[UIKeyboardFrameEndUserInfoKey]?.CGRectValue() ?? CGRectZero
            insets.bottom = (rect.size.height - (CGRectGetHeight(self.view.frame) - CGRectGetMaxY(self.textView.frame)))
            self.textView.contentInset = insets
            self.textView.scrollIndicatorInsets = insets
    }
}


func keyboardWillHide(notification: NSNotification) {
        self.textView.contentInset = UIEdgeInsetsZero
        self.textView.scrollIndicatorInsets = UIEdgeInsetsZero 
}

This stuff works great, if text in UITextView doesn't contain any empty lines. If it do, contentOffset jumps to another, random place.

I'm not sure if this is a bug in iOS 7+, or I am doing something wrong. If it's not a bug, how to get this going fluently without the jumping behaviour?

Thanks for your help.