Mine is sticking quite a bit, and the temp will go 7 degrees too warm before it finally starts up. Once it's running, it takes it several hours to bring down the readings to the right levels, especially on cooler days with no wind, hot days or windy days, it's better, but still a little warm.
I will have to look at the dual panel closely over the next week and see what happens on bright days. Today it behaved much as you have described.
But I still saw the "sawtooth" swinging temp throughout the day.