This is a great conversation, it's kept the subject in the back of my mind. Here's what I've come up with:

If you break your leg, you might be embarrassed about how you tripped over your own two feet. But i don't think you'd feel shame because the cast is a signal of a temporary condition. The broken leg says nothing about your future abilities. Contrast that with a leg that works just fine but looks different in some way- scars or a chronic skin condition. What I'm thinking is the temporary condition doesn't produce shame but when it seems like a permanent thing, it can become a feature of "self." I know some people would look at the second situation the same way as the first. But i think a number of people would internalize it. Maybe that's the difference? I don't know, I'm just thinking out loud.