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user_id=6380

The problem really lies with reload(); pickle is just one of
the many victims. E.g. this fails too:

import foo
x = foo.C()
assert isinstance(x, foo.C) # OK
reload(foo)
assert isinstance(x, foo.C) # Fails

If you have a suggestion for how to warn about reload(),
please submit a *new* bug report with Category set to
Documentation.