iOS5: Exception on UIWebView in modal UIViewController playing Youtube video

UPDATE: No longer occurs on iOS 6 beta 1

I am currently working on adapting an existing iOS 4 application with the new iOS 5 SDK. I found a new crash when presenting a UIWebView in a modal view controller that reads a Youtube video.

Starting to read the video is fine, but when I try to set it in full screen, I get the following exception :

Exception: UIViewControllerHierarchyInconsistency,
child view controller:<UIViewController: 0x6aef180> 
should have parent view controller:<WebViewController: 0x6a706c0> 
but requested parent is:<MPInlineVideoViewController: 0x6ae5d40>

Here is how I instanciate and present my modal view controller in my main view controller :

- (IBAction)buttonReleased:(id)sender
{
    WebViewController *webVC = [[WebViewController alloc] initWithNibName:@"WebViewController" bundle:[NSBundle mainBundle]];
    webVC.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
    webVC.modalPresentationStyle = UIModalPresentationPageSheet;
    [self presentModalViewController:webVC animated:YES];
}

I use the UIModalPresentationPageSheet as modalPresentationStyle, when I set this value to UIModalPresentationFullScreen, the error no longer occurs.

In my modal WebViewController, here is how I load my Youtube video :

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.youtube.com/watch?v=bDlm3eLRut0"]]];
}

Any ideas on this problem ? I can provide a full sample code that isolates this crash if needed.

Thanks !