Would someone please 'splain this climate control to me???!!!

[X5Dawg]

First off, I have the auto climate control and I only use one key so this is not a programming issue. Why is it sometimes I get in the car and the settings are set to where I left them last and other times the settings revert back to the way they were before I changed them the last time I was in it. For example:

1) I get in and the air is set at 75F, blowing on my feet and at my face.
2) I decide to change it to 72F and blowing only on my feet.
3) I shut off the vehicle and leave for awhile
4) I come back and crank up the car

Sometimes it goes back to Step 1, sometimes it goes back to Step 2

Does it have something to do with how long I am gone, how long since I changed it, what??? I have had this car for over 2 years and still have not figured this out and yes, I have searched the manual a few times.

Thanks in advance!!!