filter_format_load doesn't seem to populate $format->filters - bug or feature?

I find that you cannot simply load a format with filter_format_load() and then save it again with filter_format_save(). If you do, the filter configuration (which filters the format uses) are completely lost. This is with D7.8 at least - I am not sure if it's a bug or deliberate behaviour.

Here's my work-around:

// Load the format we want to work with.
$format = filter_format_load('my_format');

// Work-around for what *seems* to be a bug somewhere in Drupal filter
// format loading/saving.  There's probably a better way, but this seems to work.
if (empty($format->filters)) {
  // Get the filters used by this format.
  $filters = filter_list_format($format->format);
  // Build the $format->filters array...
  $format->filters = array();
  foreach($filters as $name => $filter) {
    foreach($filter as $k => $v) {
      $format->filters[$name][$k] = $v;
    }
  }
}

// Do whatever processing is required before saving.
// ...

// Save the updated format.
filter_format_save($format);