UIScrollView自动滚动64点

我正在添加UIScrollView一个UIViewControllers view.由于某种原因,在将滚动视图添加到视图并显示之间,将contentOffset设置为{0, -64},64是状态栏的20加上导航栏的44点(我猜).下面是一些重现问题的代码和图像.

如何阻止iOS设置contentOffset？

- (void)viewDidLoad
{
    [super viewDidLoad];

    _scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(10, 100, 100, 100)];
    _scroll.backgroundColor = [UIColor greenColor];
    _scroll.delegate = self;

    UIView *red = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
    red.backgroundColor = [UIColor redColor];
    [_scroll addSubview:red];

    [self.view addSubview:_scroll];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    // outputs {0, -64}
    NSLog(@"%@", NSStringFromCGPoint(_scroll.contentOffset));
}