Parallax effect and menu background

[lifeisfoo]

When I tilt the phone horizontally, a blank background appear on the left (or on the right if I tilt it in the opposite direction). Obviously, if I disable the parallax effect (and the horizontal bounces) this behaviour disappear.

Here is an example:

The gradient background is declared inside the viewDidLoad method of the menu controller:

        self.view.backgroundColor = UIColor.greenColor()
        gradientLayer.frame = self.view.bounds

        let color1 = UIColor.yellowColor().CGColor as CGColorRef
        let color2 = UIColor(red: 1.0, green: 0, blue: 0, alpha: 1.0).CGColor as CGColorRef
        let color3 = UIColor.clearColor().CGColor as CGColorRef
        let color4 = UIColor(white: 0.0, alpha: 0.7).CGColor as CGColorRef
        gradientLayer.colors = [color1, color2, color3, color4]
        gradientLayer.locations = [0.0, 0.25, 0.75, 1.0]

        self.view.layer.insertSublayer(gradientLayer, atIndex: 0)

Do you have any hint for this?