How does the Human Sensor (Energy Saving) feature work and what can cause it to detect incorrectly?

If no one enters the room for approximately 20 minutes, the Energy Saving program automatically adjusts the set temperature — increasing it by up to 4°F (2°C) in Cool/Dry mode or decreasing it by up to 8°F (4°C) in Heat mode; when someone returns, it reverts to the original settings. The sensor may fail to detect people if room temperature is high (88°F/30°C or above), if a person is not moving, or if someone is hidden behind furniture or glass. It may incorrectly detect people when pets are moving, curtains are blowing, or heating appliances are operating. (Page 8)