Hi! my HTPC is pretty basic: Intel Celeron 4th gen (Haswell), Asrock motherboard with B85 chipset, 4 GBs of DDR3 and a 3 TB Caviar Green HDD.
When I choose to shutdown, I can see systemd going all the way to "shutdown", I can hear the HDD stopping, but the PC remains on. I can still see the shutdown text on screen and hear the fans.
If I start the system, do nothing, and then shut it down, it works. If I normally use it (watch youtube or videos), then I can't shut it down without holding the power button.
Had the same problem since Kodi Isengad (shutdown process worked fine on Kodi Helix).