Stalling question, sort of odd..

The car is a 65 Valiant V200, stock 273 2bbl, auto. The transmission is that one year only: column shift, but has cables going into it.
It has just been happening recently, and doesn't happen all the time, in fact, it rarely happens. Say I've been driving for a while, and I stop somewhere, and shut off the engine. When I start it again, and put it in reverse, as soon as I start rolling backwards, the car will stall. Put it in Park, start the car again, put it in reverse, roll backwards a bit, stall. This does NOT happen ever when putting it in Drive. And this does not seem to happen if I keep the car running, and say do a 3 point turn, and put it in reverse, then drive, etc. Only when I start it up, warm, and put it in reverse.

Any ideas?