I just did a test, maybe it will help.
I turned off Num Lock. Logged off, then logged back on. Num Lock was still off.
Rebooted and logged backed in. Num Lock was still off.
Then..
Set Num Lock on and logged off and back on, Num lock still enabled and stayed that way during a reboot.
So, try turning on Num Lock then log off and back on..maybe it will hold.