A question on this topic:
In Older days (Vista and possibly Win 7), if NVDA was not set to run on the logon screen, it would also not read UAC dialogs or applications that ran under elevated privileges.
Unless that was just a fluke of my machines.
Anyway, I just tested under Win 10, and found this no longer to be the case. If I remove NVDA from the logon screen, reboot and log in, it will still read UAC screens, although it does so with the saved configuration that was in effect for the "use on logon and other secure screens", as I can determine from the differing speech rate and volume.
I had thought (but never had it confirmed), that in order to run on the logon and other secure screens, a separate instance of NVDA had to run. If that is the case, then the behavior I experienced in Vista seems reasonable. However if that's the case, how is it running now that I have removed NVDA from the logon screen, presumably disabling the ability for that instance to run with administrative privileges?
Not that I'm complaining, but I am curious.
I ask because this might in some way be related to the original question about NVDA failing to stop running on the logon screen. Then again, i could be totally off base about how this works, and it may not be related in the slightest.
I also wonder if you have tried enabling it to run on the logon screen, rebooting, and then disabling it again.