Originally Posted by
MikeWMass
I agree in principle with this, and especially with the last statement that if it worked OK at the same length before, the length should be ok now. However, if the chain should be way too long, there will be slack somewhere, and it will be on the run from the driving to the driven sprocket (the chainrings are sprockets, after all, at least for the purposes of this discussion). When you are pedaling, the slack will be on the bottom, when back pedaling, it will be on the top, as no system is frictionless. In my limited experience with this, the chain has to be quite a bit too long to cause skipping or jumping, though.
You describe the basics fairly well, but need to refer back to the OP. He had chainring autoshifting, not skipping when the chain was long, and backpedal top loop slack when back pedaling when it was short. Theory is sound, but you then have to apply it to the correct situation.