Your memory is not fading and I was one of the people making that claim.
If it were possible to disconnect the LCD physically from the circuitry immediately after the DM42 is powered down, the remanent image would persist a lot longer. What actually happens is, some of the charge within the LCD leaks out to the rest of the DM42 -- we're probably talking picoamperes here -- but it's enough to make that image fade away after maybe 1/2 hour.