Honeywell Thermostat YTH8320ZW1007/U coin battery

I just noticed that if the power goes out and then comes back, my thermostat returns to a screen asking to set date and time. Instruction manual says this is because the coin battery CR2032 is low and needs to be replaced. However, I did this and it didn’t make any difference. I also tested the battery and it was good. Do you think my thermostat is defective? By the way, it has been doing this since brand new and I didn’t know it was supposed to remember the time and date if the power went out.