Ultimate Cron uses 'cr' as a drush alias for 'cron-run' and shouldn't.

Ultimate Cron uses 'cr' as an alias for 'cron-run' and shouldn't. Drush cr rebuilds cache.

$items['cron-run'] = array(
    'description' => "Run cron job",
    'arguments' => array(
      'name' => 'Job to run',
    ),
    'options' => array(
      'force' => 'Only effective when cron-run is run without any arguments. This options skip the schedule check for each job. Locks are still respected. This option is a synonom for --options=bypass_schedule',
      'check-schedule' => 'Checks the schedule when running a single job. The opposite of --force but for a single job only',
      'options' => 'Custom options for plugins, e.g. --options=thread=1 for serial launcher',
    ),
    'examples' => array(
      'drush cron-run node_cron' => 'Run the node_cron job',
      'drush cron-run --options=thread=1' => 'Run all scheduled jobs and instruct serial launcher only to launch thread 1 jobs',
    ),
    'aliases' => array('cr'),
  );