I happened to see this on my car a few weeks back and am just getting to search for the answer. I see there are two other references to this from a HAH and a HCH I. They both list that this occurs when an "abnormality in the Tranmission Control Module (TCM) is noted." Also, "A table that starts on 14-7 of the manual list a whole multitude of malfunctions that cause the indications you described."

This has happened exactly twice and it was the same situation both times. I was near the top floor of a Parking garage and started the car, drove around until reaching the Down levels (maybe 200 ft of driving) and then I slowed to 6 mph to engage Auto Stop. This worked and I was coasting down the ramps silently but then I noticed the Drive indicator was blinking. The first time I was a little nervous but kept coasting down another few floors until I stopped the car, put it in Park, shut it off, started it again. I have forgotten if this cleared it or not.

The second time was a few weeks later and I engaged Auto Stop and coasted down the ramps. When I got the blinking Drive indicator I just ignored it. I stopped at the bottom to pay my ticket, took my foot off the gas and the engine started (still with blinking Drive indicator), and drove 8 miles home all with it blinking "D" at me. it hasn't happened since then and there were no ill-effects in FE while this happened. I did not take it anywhere to have the Codes read.