This is what I expect: I expect the get_shared_from_derived call to work, since the _internal_accept_owner would visit it. I would also expect the call to get_shared_from_base to fail with a bad_weak_ptr, since it looks like there is only one call in shared_ptr's constructor. I expect that the actual behavior is probably undefined, since it would depend on which association the compiler feels more strongly about: the enable_shared_from_this<derived> from derived or the enable_shared_from_this<base> from base. What I expect is, of course, not happening, which is why I turn to the Boost gurus. Neither of the calls work: they both fail with a bad_weak_ptr. Why would this happen?
FWIW, with VC10 get_shared_from_base() works correctly (because weak_this_ in enable_shared_from_this<base> is initialized).