I think what happen with the second finger that is being draged is that the soft bind looked for all the surface that is close to the joint. Try selecting "closest point" instead of "closest distance" under Bind method inside the smooth bind options. Also try reducing the max influence to 1. I'm wondering something... what's the scale of that hand? I ask because since it's a hand you might have modeled very small to be at scale with the rest of the model, and that means all joints are very close and so it's easy to get that kind of problem. I would model the hand really big (the same size as the body) and then one everything is cool I just resize it to fit the scale of the body. But I don't know... I'm just a noob :p
I have no idea of what's causing the deformation on the first finger though