In includes/image_utils.php find:
function resize_image_im($src, $dest, $quality, $width, $height, $image_info) {
global $convert_options;
Insert BELOW
if ($image_info[2] == 1)
{
$command = $convert_options['convert_path']." ".$src." -coalesce ".$dest;
system($command);
if (file_exists($dest)) $src = $dest;
}
Tested on windows server.