> If there is a chain A -> B -> C -> D -> E, after assignment C.__context__ = A we will get a chain C -> A -> B -> D -> E. No exception is lost.

What to do when you try to chain "C -> C"?  

I'm not sure I like this reordering idea -- it might introduce some *very* hard to find bugs -- you expected one type of exception, then you used some external library, and after that you have a completely different exception.