改变SKScene导致游戏滞后

Question

我正在使用Swift在iOS Spritekit中开发游戏。我创建了一个菜单，然后我称GameScene出现了混乱的滞后 但！如果我只加载游戏场景一切正常，如果我加载游戏，并改为另一个场景，则会造成滞后。
我在iPhone 5（iOS 8.1.x / 8.2 beta）Xcode（6.1.x / 6.2 beta）上进行了测试。在模拟器中一切都好 你可以在这个简单的代码上看到：

import SpriteKit

class GameScene: SKScene {
    let kMovementSpeed:CGFloat = 3.8
    var firstX:CGFloat = 0
    override func didMoveToView(view: SKView) {
        self.backgroundColor = SKColor.whiteColor()
        self.anchorPoint = CGPointMake (0.5,0.5)
        self.physicsBody = SKPhysicsBody (edgeLoopFromRect: self.frame)
        addBall()
    }
    func addBall(){
        var ball = SKShapeNode(circleOfRadius: CGFloat(30))
        ball.name = "ball"
        ball.fillColor = .redColor()
        ball.position = CGPointMake (-200, 0)
        ball.physicsBody = SKPhysicsBody (circleOfRadius: 30)
        self.addChild(ball)
    }
    override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
        var  touch:UITouch!
        touch = touches.anyObject() as UITouch
        let location = touch.locationInNode(self)
        if ((location.x <= 0) & (location.y <= 0)) {
            firstX = location.x
        }
        else if ((location.x >= 0) & (location.y <= 0)) {
            var ball = self.childNodeWithName("ball") as SKShapeNode
            ball.physicsBody?.applyImpulse(CGVector(dx: 0,dy: 113))
        }
        else if ((location.x <= 0) & (location.y >= 0)) {
            var ball = self.childNodeWithName("ball") as SKShapeNode
            ball.removeAllActions()
            var game:GameScene!
            self.removeAllActions()
            var moveSequence = SKAction.runBlock({
                game = GameScene(size:(self.view?.frame.size)!)
                game.scaleMode = .AspectFill
            })
            self.runAction(moveSequence, completion: {
                self.view?.presentScene(game)
                return
            })
        }
    }
    override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
        for touch: AnyObject in touches {
            let location = touch.locationInNode(self)
            if ((location.x <= 0) & (location.y <= 0)) {
                var ball = self.childNodeWithName("ball") as SKShapeNode
                let ySpeed = ball.physicsBody?.velocity.dy
                ball.physicsBody?.velocity.dx =   kMovementSpeed * (location.x - firstX)
            }
        }
    }
}

左上角 - 代表场景 左下角 - 简单的操纵杆。
右下角 - 跳跃。

我做错了什么？