In addition to the laptop mentioned in bug 80211, my desktop also fails to power off after shutdown, when acpi is not disabled in the kernel command line. /proc/acpi does not exist in either machine. I'm attaching the output of dmidecode on the desktop.
Created attachment 88858 [details] Output of dmidecode on my desktop
*** This bug has been marked as a duplicate of 82123 ***
Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.