How to resolve weird auto-logout issue?

Synopsis

Since upgrading to Yosemite, when my MacBook automatically turns it's screen off to conserve energy it also logs out which bugs me because all of my processes are killed off; this never occurred on Mavericks.

Also, since upgrading to Yosemite why is there now two log-in screens?

• When the machine is booted there is one login screen;


• When the machine is powered on from sleep mode you instantly need to login, then once the mac has booted and all devices are loaded (after ages) you need to login a second time;