Blend file: http://pasteall.org/blend/index.php?id=51691
I’ve run into an issue where a bone seems to be influencing vertices it shouldn’t. If you open the .blend file and go into weight paint mode, you’ll see the influence for the bone thoracic ends at the bottom of the rib cage. However, if you rotate that bone, the edge loops beneath it in the waist area move as well. Those vertices should only be affected by the lumbar bone.
I’ve tried removing the problematic vertices from all groups, then reassigning them by various means (weight painting with and without auto-normalize, the vertex group section of the object data panel). Removing the vertices from all groups works, but as soon as I add them to the lumbar group by any means, they start misbehaving again. I’ve gone through all the other bones to make sure none of them have some minuscule influence. This is the only part of the model where I’ve had this problem.
Can anyone figure out what’s causing this?