The point is not whether you can use VS or Level Change and the 3 times table - it's that there appears to be a bug somewhere in the software and I'd like to know both what might cause it and solutions to it. As I said, I would rather fly an NPA on VNAV than VS and this doesn't do much for confidence in the system. Does this bug only affect idle descent paths? Or does it also affect the FMC "On Approach" logic?