The problem, and why it only shows up for some people, is that disk activity resets the idle counter. If your bitrate is high enough, or you haven't lowered your idle time and your total file bitrate is ~380 (rough, rough estimate by me, could be considerably less, but for example 256 video 128 audio) you'll probably spin the disk often enough to prevent idle shutdown, which is why it didn't happen for a lot of people.
But it's certainly a problem.