The camera should recall and maintain its presets even after being left running for extended periods.
I would try restoring the defaults on your camera. If you have the IR remote you can press *, then #, then 6 to trigger the Restore.
You can also open the OSD menu and Restore Default will be the last option in the menu.
Doing the Restore will erase your saved presets and reset saved camera settings.
I would also recommend upgrading your camera to the latest firmware version. You can download the latest firmware from the Firmware Finder.
After doing the restore and updating the camera try resaving your presets and see if that prevents the drifting issue.
If you are still experiencing the issue please let us know.
You can reach out to support directly by Submitting a Ticket.