Do not know which system handles it, but it does not look like the plasma desktop can turn off screen lock.
At work this is fine - although I usually manually lock when I walk away from system
but at home this is a fatal (potentially for the hardware) problem because it will cut in during normal usage (eg: watching movies) as well as overnight if an alarm has set, making for much higher stress if one can't shut things off in a timely manner.
I'd file this as a fatal flaw only because one of us is likely to take a sledgehammer to the computer if it's not fixed soon.
ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: plasma-desktop 4:5.2.2-0ubuntu4
ProcVersionSignature: Ubuntu 3.19.0-26.28-generic 3.19.8-ckt4
Uname: Linux 3.19.0-26-generic x86_64
NonfreeKernelModules: fglrx wl
ApportVersion: 2.17.2-0ubuntu1.3
Architecture: amd64
CurrentDesktop: KDE
Date: Mon Aug 24 09:39:16 2015
InstallationDate: Installed on 2013-09-28 (695 days ago)
InstallationMedia: Linux Mint 15 "Olivia" - Release amd64 (20130520)
SourcePackage: plasma-desktop
UpgradeStatus: No upgrade log present (probably fresh install)
turns out to be a UI bug. It's possible to disable if one sets timeout to 0????
(took hunting through forums to find that out - it's certainly not information present in any form on the UI itself)