Boost module remove all caching files without "Purge expired cache files on cron runs"

My Boost module on drupal 6 works fine for caching anonymous users page calls in static files. In current version I have set the option "Purge expired cache files on cron runs" to deactivate! But on every cron run (in my case all full hour) the static file cache is dropped!
I think, the option-check in boost_cron() works fine, but I think there is a bug in the boost_flush_caches(). In that the method boost_cache_clear_all() will be executed without check..

Could that work for you?

function boost_flush_caches() {
if (variable_get('boost_expire_cron', TRUE) && (variable_get('preprocess_c    ss', FALSE)==TRUE || variable_get('preprocess_js', FALSE)==TRUE)) {
boost_cache_clear_all();
} 
  return;
}

Need urgent help!