Running OpenSUSE 13.1 with Kernel:Stable

    uname -a
        Linux gktest 3.17.2-1.g1afb260-desktop #1 SMP PREEMPT Thu Oct 30
19:14:09 UTC 2014 (1afb260) x86_64 x86_64 x86_64 GNU/Linux

and latest systemd

    systemctl --version
        systemd 210
        +PAM +LIBWRAP +AUDIT +SELINUX -IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT
+ACL +XZ +SECCOMP +APPARMOR

where 'shutdown' and 'reboot' are controlled via systemd

    ls -al `which reboot` `which shutdown`
        lrwxrwxrwx 1 root root 18 Oct 30 08:32 /sbin/reboot ->
/usr/bin/systemctl*
        lrwxrwxrwx 1 root root 18 Oct 30 08:32 /sbin/shutdown ->
/usr/bin/systemctl*

on exec of either

    systemctl poweroff
    shutdown -h now

the system shutsdown, then immediately restarts.

Forcing and ungraceful shutdown

    systemctl --force poweroff

does, in fact completely powerdown the machine.

This is a change in behavior from 3.16.x kernels, which shutdown correctly.  
Unclear what, if any, other earlier dependencies were involved.

Currently, acpi setup reports @ boot

    dmesg | grep -i acpi
        [    0.000000] Command line: root=/dev/VG1/ROOT rootfstype=ext4  
rootflags=journal_checksum noresume showopts selinux=0 SELINUX_INIT=NO
apparmor=0 elevator=cfq console=tty0  clocksource=acpi_pm divider=10 nomodeset
pcie_aspm=off noquiet nolapic_timer  systemd.log_target=journal-or-kmsg
systemd.log_level=info net.ifnames=0 biosdevname=0 acpi_backlight=vendor
acpi_osi=Linux vga=0x318
        [    0.000000] ACPI: Early table checksum verification disabled
        [    0.000000] ACPI BIOS Error (bug): A valid RSDP was not found
(20140724/tbxfroot-211)
        [    0.000000] Nvidia board detected. Ignoring ACPI timer override.
        [    0.000000] If you got timer trouble try acpi_use_timer_override
        [    0.000000] Kernel command line: root=/dev/VG1/ROOT rootfstype=ext4 
 rootflags=journal_checksum noresume showopts selinux=0 SELINUX_INIT=NO
apparmor=0 elevator=cfq console=tty0  clocksource=acpi_pm divider=10 nomodeset
pcie_aspm=off noquiet nolapic_timer  systemd.log_target=journal-or-kmsg
systemd.log_level=info  net.ifnames=0 acpi_backlight=vendor acpi_osi=Linux
vga=0x318
        [    0.112000] ACPI: Interpreter disabled.
        [    0.142996] pnp: PnP ACPI: disabled
        [    5.514180] ata1: nv_mode_filter: 0x1f39f&0x1f3ff->0x1f39f,
BIOS=0x1f000 (0xc5000000) ACPI=0x0
        [   16.891450] ACPI Exception: AE_BAD_PARAMETER, Thread 3394323792
could not acquire Mutex [0x1] (20140724/utmutex-285)
        [   16.954440] ACPI Exception: AE_BAD_PARAMETER, Thread 3394323792
could not acquire Mutex [0x1] (20140724/utmutex-285)
        [   40.895801] NVRM: failed to register with the ACPI subsystem!

Fyi, this kernel bug,

    [PATCH]Poweroff doesn't work, it just reboots
    https://bugzilla.kernel.org/show_bug.cgi?id=66171

identifies the same symptom, but seems to link the cause to xhci/USB3 drivers. 
I have no USB installed.

Not clear what diagnostic info is helpful; can provide whatever on request.