I've noticed that the Sleep Timer doesn't seem to power down my iPod unless the iPod is in either Play or Pause mode - in Stop mode the timer expires and the iPod remains powered on. (This is while running on battery, not plugged in, of course.) And here's the funky part: When the timer expires in Stop mode and the iPod remains powered on, if you then start a track playing, THEN the iPod immediately shuts itself down.
This is with an ipod6g running dev build c5103bab95-250127 and an ipodvideo running dev build 8aa54286c4-250125. Both are flash modded with 256GB.
Honestly, I'm not working overtime looking for obscure bugs, but I guess I tend to do stuff in dark corners on the fringes where other users don't go. In this case I was doing some digging, looking for specific conditions that result in the "white flash at shutdown" that I started experiencing with either dev build f42343b715 or 734cc3e8d1 [https://forums.rockbox.org/index.php/topic,55159.msg255067.html#msg255067]. But this Sleep Timer thing goes back at least as far as dev build 50515de940-241222 which I also tested today from a backup I have of that build, so it seems unlikely that the Sleep Timer and white flash are related (though what do I know?).