KDE: Leave --> Turn Off Computer not shutting down system

I've searched /var/log/ for any shutdown-related errors

Debian 8 using systemd, you should check ERR log with journalctl -xb

The release news says:

"Jessie" ships with a new default init system, systemd. The systemd suite provides many exciting features such as faster boot times, cgroups for services, and the possibility of isolating part of the services. The sysvinit init system is still available in "Jessie".

I am confused It would say No journal files were found.
You can check whether systemd-journald is running withsystemctl status systemd-journald And start it with:

systemctl enable systemd-journald
systemctl start systemd-journald

This is a known bug affecting HP EliteBook laptops:

• Bug#775519: System reboots instead of shutting down on HP EliteBook 840
• Bug#775812: base: HP EliteBook 840 G1 laptop fails to halt/poweroff after 15/12/2015 upgrade

The bug appears to be in the kernel and as such affects other distributions as well.