As I said to you Adam, I am not enjoying the unique problem you are. I set it, reboot, shut down, sneeze 5 times or more and nothing changes. I can set it at 50%, 60% or 100% and it remains where I set it.
It must be the Model I have and this one came with Windows 8.1 and I've been updating of course with each new update. I hope you can get that solved but if it is indeed entirely dependent upon Microsoft, the wait might be long, although I hope that is not the case.
The NVIDIA card in this is a Geoforce GTZ 765M and it's updated as soon as the new updates tear on down through the tubes.