Imagemagick exec problem in Windows

There is bug when running Drupal+Imagemagick in windows. PHP's Exec function does not work correctly in Windows then I have added exec wrapper that detects current mode and I Windows are detected then uses POpen. This code is taken from php.net exec function manual.

function _image_exec($cmd) {
  if (substr(php_uname(), 0, 7) == "Windows"){
    if ($h = popen("start \"bla\" $cmd", "r")) {
      pclose($h);
      return true;
    } else {
      return false;
    }
  } else {
    return exec($cmd);    
  }
}