I would have to let my system run for a while to test but there is a possibility, if you system is needing more processing time than is being allowed, that it might change the settings. I do not know this to be a fact, but just a thought.
You might try a higher setting and see if it holds longer. If it is being changed, then you might check it after doing something like watching a video or playing some game, or multitasking.
Exactly how the setting is meant to work with multiple core systems, I am not sure. But most systems today do keep their processors running a little as possible. Task Manager or the Resource Monitor, may give you some information about how your processor is behaving. There have been situations were some...