There are really two forms of seat memory, as follows:
1) The setting on the side of the driver's seat can be programmed by setting the seat where you want it, then press the memory button followed by which memory button you want to set 1, 2 or 3. Once set, if your seat is ever moved just hold down the memory button you programmed and your seat will return to where it was set.
2) Key seat memory (as per your post) is set by the last position the seat is at when you lock the doors using your key remote. When you open the doors with the same key, the seat will return to the last setting for that key. If you're the only driver, nothing needs to reset. If someone else has a key to the car and changes the seat setting, when you return and open the doors, the seat will return to the last setting recorded with your key.
1) and 2) above work independently of each other. So, if for some reason another person uses your key (i.e. wife, friend, etc.) changes the seat setting and later locks the doors with that setting, when you return, the seats will be set to the other persons setting. In this case just use the seat memory on the side of the seat to go back to your setting, then when you lock the doors the key is again set to your setting.
Hope this helps.