I took a peek through the vents at the bottom, but I can't tell if it is a light frost or ice, but I don't want to start taking off the panel and looking now and making it worse.
In test mode, I am happy to report that it shows that it has been defrosting (whether it actually HAS or not has yet to be determined). It shows in the last 72 hours (or since Friday night when I had it unplugged changing out the therm) that it has defrosted twice. First time showed that the duration was 8 minutes, the latest time was 9 minutes. Also, the D no longer flashes.