Screen corruption after dismissing modal UIImagePickerController subclass - iphone

Question

I am having trouble dismissing a modal view controller containing a UIImagePickerController (ZBarScannerController). For some reason, after dismissing the controller after scanning a bar code with the iphone camera, the view controller always leaves a rectangle of stale graphical data over the same area as the ZBarScannerController's tool bar. The corrupt data is always a portion of whatever image the camera was seeing at the moment.
An image of the problem (corrupt area in red rectangle):
It is impossible to remove that rectangle of corrupt screen data except by backgrounding / killing the app. Also, if I specify NO when I dismiss the modal picker, the OS will remove the view controller while still displaying the controller on screen, causing crashes if I interact with any controls on the modal view. How can I go about fixing the problem?
Code for dismissing the controller:
- (void) imagePickerController: (UIImagePickerController*) reader
didFinishPickingMediaWithInfo: (NSDictionary*) info
{
id<NSFastEnumeration> results =
[info objectForKey:ZBarReaderControllerResults];
for (ZBarSymbol *oSymbol in results) {
//process result
//Ensure that QR code is decoded
zbar_symbol_type_t type = oSymbol.type;
if (type == ZBAR_QRCODE) {
//Get Barcode Data
NSString *dataStr = oSymbol.data;
[self processCommand:dataStr];
}
}
//[reader dismissModalViewControllerAnimated:NO];
[[m_oReaderController parentViewController] dismissModalViewControllerAnimated:YES];
}
Code for making the controller:
- (void)onQRCameraActivate:(id)sender {
IPOProofAppDelegate *oAppDelegate = (IPOProofAppDelegate *) [[UIApplication sharedApplication] delegate];
if (m_oReaderController == nil) {
m_oReaderController = [[ZBarReaderViewController alloc] init];
m_oReaderController.readerDelegate = self;
ZBarImageScanner *oScanner = m_oReaderController.scanner;
[oScanner setSymbology:0 config:ZBAR_CFG_ENABLE to:0];
[oScanner setSymbology:ZBAR_QRCODE config:ZBAR_CFG_ENABLE to:1];
}
[self.navigationController presentModalViewController:m_oReaderController animated:YES];
}