I have a short IK chain with an IK constraint with stretch enabled. The bones in the chain each have their Inverse Kinematics Stretch set to 0.001. Here's a simple demo setup...
Moving the Control bone around within reach of the IK chain seems to work fine. E.g.
But when I cause the stretch to take effect by moving the target out of reach of the IK chain, the chain stretches and scales in all 3 dimensions causing the mesh to expand. Note the size of the mesh and IK chain bones relative to the target as compared with the other images.
Is there some way to only have this stretch along the Y axes of the bones? I.e. I want the bones and mesh to elongate but not swell. I have tried various other settings, including locking X and Z scaling on the bones.
You can grab a .blend file of the sample setup at http://readyposition.com/Blender/IKStretchExperiment.blend