The current behaviour is the result of how I interpreted the error
reporting specification in PEP 3134. See "Enhanced Reporting" in
http://www.python.org/dev/peps/pep-3134/ . I may have misinterpreted it,
in that both the cause and the context are printed out while the PEP may
be read as suggesting the context must not be printed out when there is
a cause.

In any case, I don't think it is a release blocker. It only regards a
new and advanced feature (explicit exception chaining) and doesn't
disrupt its functioning.