Stopping a Schedule

I always thought that doing $schduleID.delete(); would stop the schedule from being processed. It doesn't seem to be working however. Anyone know how to stop a schedule?

Example:

function Start()
{
$id = schedule(100, 0, stop);
}

function stop()
{
if (isObject($id))
$id.delete();

//do stuff
}

function thisMayBeCalledBeforeTheSchduleTimeIsUp()
{
stop();
}

If I call "thisMayBeCalledBeforeTheSchduleTimeIsUp()" the old schdule ($id) will call stop again when the time runs out. (Even removing the isObject() check failed to work).

[EDIT]
It seems $id will track the schedule (and I can stop it) only once. I can not assign another schedule to the same var. Wierd...