Something has happened to Win 8.1 fairly recently which causes last person who was on the pc to 'sign in' automatically on boot up even if none of my three users are signed in.

Instead of going to the 'sign in screen' it briefly displays the screen then goes to the last person signed in.

I dont want this as I invariably have to sign the other out or go find mine.

Wondering what has been customised in settings?