I have a 2005 Honda Accord with original radio. The problem is that it doesn’t save any radio station presets. Well, sometimes it does, it seems like when the engine is hot and I program the stations then it saves them, but never overnight or longer periods when the engine is switched off. And it’s only the radio station presets that will go, the other settings are fine.
I would say that as it is saving the other settings that it is getting a constant live from the battery.
And assuming that no on has messed around with the wiring all SHOULD be well. However it's clearly not so i would guess that this is an internal issue and only reoslution would be a replacement unit.
However, in some cases where the wiring has been 'altered' then both the constant live and ignition/accessory live are wired together to the ignition/accessory live meaning that once the ignition is tunred off, then all settings are lost.
I hope this helps but i can't think of any other reason, other than an internal fault that would cause this.