In Lion I always used Control ⌃+Shift ⇧+Eject ⏏ to put my display to sleep when I walked away from my computer. The system would continue running and not go to sleep.
Now in Mountain Lion when I put the display to sleep, the system sometimes decides to go to sleep as well.
It does not happen all of the time, it has been rather unpredictable. Some times I walk away for 2 minutes and come back and it went to sleep entirely. Other times I walk away for hours and come back and it did not go to sleep.
Very odd. Any ideas?
EDIT
Screenshots for both Power Adaptor and Battery Energy Saver settings.
Also I just experienced the issue again. I walked away for about 3-4 minutes and came back and WiFi was disconnected so it does not seem like the Energy Saver settings are being respected.
Unless... Energy Saver is considering the 15 minutes have elapsed being that my Display has gone to sleep and is therefore kicking in the computer sleep Energy Saver setting? I will up the Computer Sleep and see what happens.