Why Won't My Schedule Cancel?

I'm trying to create a countdown that will broadcast every second (starting at 30) Game Will Start In x Seconds. It was working, but I had a suspicicion that after it had finished, it was running in the background, so I added a getLogger->info->("STILL RUNNING") and I found that no matter what I tried, the schedule continued to check every second. What is going on? (The value for the counter is stored in count.txt for the moment)

PHP:

class Countdown extends PluginTask{
    public function onRun($currentTick) {
        $sec = file_get_contents($this->getOwner()->getDataFolder() . "count.txt");
        if($sec != 0) {
        $this->getOwner()->getServer()->broadcastMessage("Game Starts In $sec Seconds");
        $sec--;
        file_put_contents($this->getOwner()->getDataFolder() .  "count.txt", $sec);
        }
        $this->getOwner()->getServer()->broadcastMessage("STILL RUNNING");
    }
    public function cancel() {
        file_put_contents($this->getOwner()->getDataFolder() .  "count.txt", 30);
        $this->getOwner()->getServer()->broadcastMessage("Game Will Now Start!");
        $this->getHandler()->cancel();
    }
}


PHP:

public function onBlockBreak(BlockBreakEvent $BBE) {
        $task = new Countdown($this);
        $this->getServer()->getScheduler()->scheduleRepeatingTask($task, 20);
    }


Reference:
https://github.com/PocketMine/PocketMine-MP/blob/master/src/pocketmine/plugin/PluginManager.php#L640 (shall be the uppermost call because this function is not specific for scheduling)
https://github.com/PocketMine/Pocke...etmine/scheduler/ServerScheduler.php#L136-137 ( https://github.com/PocketMine/Pocke.../pocketmine/scheduler/ServerScheduler.php#L41 $task is a TaskHandler instance)
https://github.com/PocketMine/Pocke...pocketmine/scheduler/TaskHandler.php#L130-140

Therefore, the correct sequence of code call to cancel an event is:

1. ServerScheduler->cancelTask($taskId) (by comparing https://github.com/PocketMine/Pocke...etmine/scheduler/ServerScheduler.php#L124-125 and https://github.com/PocketMine/Pocke...etmine/scheduler/ServerScheduler.php#L136-137 , we can see that cancelTasks(Plugin) executes code similar to cancel($taskId)
2. TaskHandler->cancel()
3. Task->onCancel()

You are calling 2., so the last part of cancelling a task (ServerScheduler->tasks[$taskId] unsetting) is skipped, so it doesn't work.