Windows 10 numlock automatically turns off after 5 seconds of no activity

keyboardnumlockwindowswindows 10

I've upgraded to win 10.
Each 5 seconds of no keyboard activity (I can move the mouse) the numlock automatically turns off.

How can I stop this annoying behaviour?

It's irritating because when I continue using the keyboard in order to write, sometimes there's a delay, because the numlock is off and the windows want it back on. It doesn't happen instantly.

Thanks.