Maybe you're drawing too fast at the end of your draw cycle. I could see how this could "catapult" your arrow off the rest.

I see you're a life member so you know what your doing, so I don't want to insult you, but is it possible that you're pulling too much weight? Sometimes being overbowed can make for an unsteady draw cycle.

I don't use dropaways, but I've seen many of them that have a hard surface that the arrow rests on. Maybe a little piece of molehair would soften it up. The arrow would be a little less responsive to a soft surface than the hard surface.