Player: VLC 3.2 64 bit
OS: Win 8.1 x64
Steps to replicate.
Start VLC with brand new profile with all the defaults, including "Disable screensaver" checked.
No problems found. Screensaver/power save does not activate.
Since I like my controls on the computer, and the video on the television, I change one setting.
In settings (all) under Video, I uncheck "Embedded video". Save the setting, close the player.
Start the player, and video is now in separate window.
Screensaver/powersave is activating.
So, it seems to me that unchecking "Embedded video" affects the "Disable screensaver" saving.