Never actually solved.
So you have Skeleton bones which are not animated.
You have a hand joint 100% controlling the fingers influence (using the skinning method inside out) and when you add influence to the fingers, the geomtry folds up and distorts for no reason. This has nothing to do with it’s weighting being incorrect, because the vertices should not move, and there is no reason why they should.
Maya 2018 btw
So how Maya SHOULD do this, is when you add influence to one bone, it subtracts away from others. Since that bone in my cast is only the hand bone, it can only take influence away from that joint.
So perhaps the weights are incorrect I hear the young student cry out…
but checking in component mode shows you the values of each independent vertex, relative to what it’s assigned too, and it shows the finger is giving 0.2 whilst the hand is correctly at 0.8
This is why this is still an ongoing MAJOR bug with Maya, and one which has never been resolved so far.
Any professional riggers who may have come across this problem here, who found a workaround please?