Ios5 是什么导致状态栏与视图重叠？

知道为什么状态栏在显示Modalviewcontroller->dismissModalViewControllerAnimated后与视图重叠吗

Xcode:4.2 SDK:iOS5 部署目标：3.2 弧：开

改为：

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    UIViewController* currentViewController = [self getCurrentViewController];
    return [currentViewController canRotate]; // the implement is exactly as same as shouldAutorotateToInterfaceOrientation:
}

解决这个问题，但我不明白为什么

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    UIViewController* currentViewController = [self getCurrentViewController];
    return [currentViewController canRotate]; // the implement is exactly as same as shouldAutorotateToInterfaceOrientation:
}