Always resizing user pictures breaks transparency?

I recently noticed that when uploading transparent user pictures to a Drupal site, the transparent colour is lost (replaced with black). I think its to do with image_size()... but I noticed the slightly odd logic in user.module:

 if (!$info || !$info['extension']) {
    form_set_error('picture', t('The uploaded file was not an image.'));
  }
  else if (image_get_toolkit()) {
    image_scale($file->filepath, $file->filepath, $maxwidth, $maxheight);
  }
  else if (filesize($file->filepath) > (variable_get('user_picture_file_size', '30') * 1000)) {
    form_set_error('picture', t('The uploaded image is too large; the maximum file size is %size kB.', array('%size' => variable_get('user_picture_file_size', '30'))));
  }
  else if ($info['width'] > $maxwidth || $info['height'] > $maxheight) {
    form_set_error('picture', t('The uploaded image is too large; the maximum dimensions are %dimensions pixels.', array('%dimensions' => variable_get('user_picture_dimensions', '85x85'))));
  } 

So, the image is always scaled if an image toolkit is found. The attached patch only scales user pictures if they are too large, and will still show an error if a toolkit is not found.

I'm aware that there may be a better patch for image.inc to retain scaled image transparency?