Probably happens every time you disconnect battery lead to the radio, unless it has some reserve power in the head unit, such as a small lifetime battery or a discharging capacitor. So it will likely happen again if you disconnect your radio unit or the car battery.
If the stations are reprogrammed, and are lost when simply turning off the key[or radio], perhaps the constant power lead on the radio is connected to the accessory[key] power from the car. Is that what is happening?
Boxcar's Nissan Cube Audio Upgrade - Nissan Cube Car Forums
i used this thread to assume on the car end, the constant power is yellow, the accessory power is red, but i have not seen them with my own eyes.
Thank you to nissancubelife.com!
I gugld 2009 nissan versa stereo wiring diagram.
Also I'm sure many here could tell you exactly which is constant [battery] power. You could also use a multi-meter. The wire that conducts with no key in the ignition is the constant power. Hope this helps. 08v