I have found that when there are sudden extreme changes of the throttle, the trans gets confused. In 1st or 2nd, a suddenly dropping the throttle at high revs will induce a hard shift that will make you think the trans is trying to drop out of the car. I have had the same thing happen with the same conditions as you have rapid on-off-on=false neutral. After you let off for a couple of seconds, the trans figures things out, decides on a gear, and away you go. I bought my SE with 63K on it, it now has 96K, and it has done the above since I got it. I have just got in the habit of never letting off suddenly in the lower gears.