I wish I could give you a definate answer.
Does it do the same deformation every time?
What I have read is maybe trying to shorten the death animation frames to 10 or less.
Also make sure the the verticies are really were they belong.
Take extra time and care in assigning them. Everything weighted.
Make sure that all verticies are welded before Skinning to get rid of Isolated or duplicate veticies.
I see this on stock models also. sometime worse depending on which shader is being used. Try with the effectbank\bumpbone\bumpbone.fx shader and see if it still happens.
I dont know if you can completely resovle it, but maybe make the deformation a bit less noticable.
Hope this helps.
Nothing but coffee in my veins 'Insomnia is Coming'
