Do you actually fly the -800?! There is no "Auto" setting on the control, the Auto refers to the entire selection I believe, as it will automatically control the zone to the tempreature setting you have selected. As opposed to "Off" where the pack controls will cause the left pack to maintain a fixed temperature of 75°F (24°C) and the right pack to maintain 65°F (18°C) as measured at the pack temperature sensor.
It controls against the tempreature sensors in the cabin, one in Row 2, one at the rear. So technically, if the cabin gets cold it should compensate to make up but I do think its one of the worst design features of the 737, especially on a cold morning when it goes wild trying to heat the cold soaked cabin!
One thing Airbus did right - put the tempreature controls out on the cabin touchscreen!