@chrishamm - finally figured this out. I was using 5V from the 6HC mainboard to power my display. During power off with M81, the 5V line voltage to the display would vary a lot (enough to cause the problems seen). Connecting the display to a separate (dedicated) 5V power source has eliminated the problem reliably. Probably should have used an O-Scope to quantify the variation; however, the cleaner power clears up the display.
