Same one. Digital. We replaced it a couple of years ago. Nothing has changed except the ac unit.
Feedback control theory says the thermostat "should" drive the temperature back to the same sensor value, no matter whether the refrigerant is less efficient or not....it "should" do that by simply running the compressor a bit longer. So, unless the thermostat's internal sensor has jumped calibration (which is certainly possible), I don't understand what is going on.