Large UIScrollView with background pattern fails

[Craig2]

I have a UIScrollView with a very large content view, it's a bookshelf with around 1000 items on it, when the scroll views content becomes more than around 16000px high it shows a black background and all graphics overlap/blend together.

Here is the sample code

- (void)viewDidLoad {
    [super viewDidLoad];

    // Doesn't work
    int sizeForContent = 20000;

    // Does Work
    //sizeForContent = 10000;


    UIScrollView *scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];  

    UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, sizeForContent)];
    subView.backgroundColor = [UIColor colorWithPatternImage: [UIImage imageNamed: @"wood.jpg"]];
    [scroll addSubview:subView];
    [subView release];

    scroll.contentSize = CGSizeMake(self.view.frame.size.width, sizeForContent);
    [self.view addSubview:scroll]; 

    [scroll release];

}

Does anyone know why this happens? I assume it is something to do with memory limits but it doesn't seem to be using much memory.

I know I could set the scrollview background color directly instead of adding a subview and setting the background of that but I need to leave the scrollview background as a color.

You can get the basic xcode project from ScrollViewTest.zip if you want to see the issue.

Any help or explanations greatly appreciated.