Carrier Infinity Control Thermostat Problem (I think)

We had a complete Infinity system installed in October - furnace, air conditioner and high end thermostat.
I programmed the thermostat to be at one temp from 6am - 10pm, and another from 10pm - 6am. Did the same for heat and cool (different temps of course). It worked fine for heat but now with the airconditioner every night sometime between 8pm and 9pm the temp starts to go down. It's supposed to be 76 until 10pm. First it will be 75, then 74, then 73 - always before 10pm. Also we have the fan set on Low all the time. On a few occassions the fan just off. In a short while it came back on by itself.
Finally, the manual says I should be able to set the fan speed at different rates for the different times of day. I do what the guide says (press Schedule and then the Fan button) but it stays on the Schedule All Days screen.
Am I crazy or does this sound like there's some techinical glitch in this thing? What I don't get is why it worked so well in the winter.
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