A morph works by telling Poser to move a specific point a certain distance in a certain direction - it's just a list of "deltas" (amounts to move up, left and forward) so it will work only when the right number of points are present, in the right order. It is extremely dumb and can't compensate for even minor changes, which is why creating a morph with a modeller that re-orders the points can produce - umm - interesting results.