Restarting restores the brightness adjust, but following any Suspend it freezes again. Only restarts work temporarily, turning off and on again has no effect.
Yes, there's something completely klutzy about this 'fix'...
I had it fall me when an MS installer called its own restart -- not bothering to try to figure out all ways this fails.
My brightness control is a key, so just lean on it on startups when required, saves this waste of time.