That's an interesting find.
On the Panasonic site, the manufacturer states this mw oven includes "inverter" technology. Mind you, this has little to do with our boats' traditional inverters, I suppose, but nonetheless I have noticed Amel and other sailboat manufacturers now install washers/dryers that also feature this "inverter" technology.
Now, when you write that the clock keeps the time, surely you mean only for as long as your boat is plugged into shore power? Or does it have a backup battery for those times when there is no 220v power supply?
Docked at Alcaidesa (Gibraltar)