UITextView宽度大于512不显示文本

每当我将 UITextView 的大小扩大到大于 512 时，代码如下：

textView = [[UITextView alloc] initWithFrame: CGRectMake(0, 0, 513, 1024)];

它不再显示任何文本... 512 可以工作，任何低于该值的尺寸也可以，但任何大于 512 的尺寸都会停止显示任何文本。完整代码：

- (void)loadView {
    self.navigationItem.hidesBackButton = YES;

    self.view = [[UIView alloc] init];
    self.view.backgroundColor = [UIColor blackColor];

    RDLocalizedStrings * strings = [RDLocalizedStrings defaultLocalizedStrings];

    NSString* message = [strings getStringWithKey: @"noUpdatesAvailableText"];

    CGFloat messageFontSize;

    RDRectCreate(message);

    BOOL iPad = NO;
#ifdef UI_USER_INTERFACE_IDIOM
    iPad = (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad);
#endif
    if (iPad) {
        RDRectWrite(message, 0, 100, 513, 200);
        messageFontSize = 20.0;
    } else {
        RDRectWrite(message, 0,  0, 320, 480);
        messageFontSize = 20.0;
    }

    textView = [[UITextView alloc] initWithFrame: messageRect];
    textView.text = message;
    textView.backgroundColor = [UIColor redColor];
    textView.textAlignment = UITextAlignmentCenter;
    textView.textColor = [UIColor whiteColor];
    textView.font = [UIFont systemFontOfSize: messageFontSize];
    textView.editable = NO;

    [self.view addSubview: textView];
}

It seem UIViewAutoresizingFlexibleWidth制作ipad的UITextView隐藏文本。调整大小textView.frame=CGRectMake(0,0,768,21)可以解决这个问题。