Download link provides useless filename

Most probably the problem is that the MIME type is not detected properly. Fileframework allows trusting the MIME type provided by the browser (some browsers does not post the uploaded file's MIME), detection the MIME on the server side (using fileinfo), which is not ideal as also does not work for all cases, or conditional - try to detect on the server side if the browser does not send the MIME.

When you saved the file in bitcache and are creating a node, the fileframwork trust the MIME type which is pulled from the bitcache:

$file->type = isset($file->type) ? $file->type : bitcache_get(file_get_hash($file->uri))->type;

This is a bitcache function which tries to detect a MIME type:

  function mime_type() {
    if (extension_loaded('fileinfo') && ($finfo = finfo_open(FILEINFO_MIME))) {
      $type = finfo_file($finfo, $this->path);
      finfo_close($finfo);
      return $type;
    }
    else if (function_exists('mime_content_type')) {
      return mime_content_type($this->path);
    }
    else if (file_exists($this->path)) {
      // Attempts to detect a file's MIME type using the Unix `file' utility.
      // MIME content type format defined in http://www.ietf.org/rfc/rfc1521.txt
      $output = exec('file -bi '. escapeshellarg($this->path), $ignore, $status);
      if ($status == 0 && preg_match('!([\w-]+/[\w\d_+-]+)!', $output, $matches))
        return $matches[1];
    }

    return 'application/octet-stream'; // default to binary
  }

try running "file -bi your_file" on the command line to see if this utility can detect LZMA type.

feel free to reopen issue