Flash Upload doesnt work when $config['SecureImageUploads']=

This is my Config.php on Flash-Position:

$config['ResourceType'][] = Array(
      'name' => 'Flash',
      'url' => $baseUrl . 'flash',
      'directory' => $baseDir . 'flash',
      'maxSize' => '8M',
      'allowedExtensions' => 'swf,flv',
      'deniedExtensions' => '');

Flash-Files over 1 MB upload correct. But my 5kbyte File doesnt upload correkt. I get a error dialog that my file is corrupt.

When i chance this option:
$config['SecureImageUploads'] = true;
in
$config['SecureImageUploads'] = false;

then the upload works fine!

Please help.