UIImagePickerController messing tabbar frame when dismissing

问题

I am trying to show a UIImagePickerController in a UIViewController inside a UITabBarController

SourceType Camera
MediaType kUTTypeMovie

There's no issue presenting the UIImagePickerController, but when dismissed the TabBar moves down half the height, it only happens sometimes... other it dismisses perfectly.

override func viewDidLoad() {

    var test: UIButton = UIButton(frame:CGRectMake(140, 200, 100, 100))
    test.backgroundColor = UIColor.redColor()
    test.addTarget(self, action:"presentCamera", forControlEvents: .TouchDown)
    self.view.addSubview(test)
}

func presentCamera(){
    if UIImagePickerController.isSourceTypeAvailable(UIImagePickerControllerSourceType.Camera){
        imag.mediaTypes = [kUTTypeMovie]
        imag.delegate = self
        imag.sourceType = UIImagePickerControllerSourceType.Camera;
        imag.videoQuality = UIImagePickerControllerQualityType.TypeMedium
        imag.videoMaximumDuration = 120
        imag.allowsEditing = false
        self.presentViewController(imag, animated: true, completion:{println("showing")})
    }

}

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [NSObject : AnyObject]) {
    let library = ALAssetsLibrary()
    var videoTemp = info[UIImagePickerControllerMediaURL] as NSURL
    videoPath = videoTemp.relativePath
    UISaveVideoAtPathToSavedPhotosAlbum(videoPath, self, nil, nil)
    picker.dismissViewControllerAnimated(true, completion:{
        println("video selected")
    })    
}

func imagePickerControllerDidCancel(picker: UIImagePickerController) {
    picker.dismissViewControllerAnimated(true, completion:{
        println("canceled")
    })
}

It is also displaying this error:

"Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates."

Here is a video of how the app and the error looks:

https://www.youtube.com/watch?v=o1BgLbZgsfw