Scheduled cron job with custom interval is unset on next cron event

[mrtphoto]

plugin adds new interval

  function execution_schedule( $schedules ) {
  // adds 2min schedule interval for all import execution script
    $schedules['twomin'] = array(
      'interval' => 120,
      'display' => __('Two Minutes')
      );
    return $schedules;
  }
  add_filter( 'cron_schedules', 'execution_schedule' ); 
}

on save options for plugin cron url, we clear the old hook and set the new cron job with custom interval

wp_clear_scheduled_hook( 'syt_trigger_one' );
wp_clear_scheduled_hook( 'syt_execution_one' );
wp_schedule_event(current_time( 'timestamp' ),'twicedaily','syt_trigger_one');
wp_schedule_event(current_time( 'timestamp' ),'twomin','syt_execution_one');

on options page I display the schedule for the hook

echo wp_get_schedule( 'syt_execution_one' );

Immediately after saving it displays 'twomin'. When loading the options page after that it shows nothing .
An output of

print_r(get_option('cron'));

confirms the existence of the scheduled cron event on save and subsequent disappearance of the hook from cron

    [1419832800] => Array
        (
            [syt_trigger_one] => Array
                (
                    [40cd750bba9870f18aada2478b24840a] => Array
                        (
                            [schedule] => twicedaily
                            [args] => Array
                                (
                                )
                            [interval] => 43200
                        )
                )
            [syt_execution_one] => Array
                (
                    [40cd750bba9870f18aada2478b24840a] => Array
                        (
                            [schedule] => twomin
                            [args] => Array
                                (
                                )
                            [interval] => 120
                        )
                )
        )

..after loading the options page again, no "syt_execution_one" hook:

    [1419832800] => Array
        (
            [syt_trigger_one] => Array
                (
                    [40cd750bba9870f18aada2478b24840a] => Array
                        (
                            [schedule] => twicedaily
                            [args] => Array
                                (
                                )
                            [interval] => 43200
                        )
                )
        )

[valendesigns]

Could you turn the code you supplied above into a basic plugin that reproduces the issue?

[mrtphoto]

I was doing some cleanup work on the plugin to share it for troubleshooting and found that my addition to the cron_schedules filter ended up inside the hook for admin_init. So, on the options page is was working. But when wp-cron ran "twomin" was no longer a valid interval and was removed.
I moved it outside admin_init and it works fine now. I'm going to assume that the removal of the cron job with an invalid interval is a feature.