I just installed my Nest thermostats (non-heat pump system). I have the sleep temperature set to 71 and I have the workday temperature set to 75. The mode is set to cool only. When the thermostat switches from sleep mode to workday mode, it turns on the heat to bring the temperature up to 75 instead of letting it naturally climb to 75 before the cooling mode turns on. Why is the heat coming on when only cool mode is selected?