bug: pickle not working in 2.2.3

I'm working with python 3.6.3 and pybind11 2.2.3, conda distribution, on ubuntu 17.10,

The following code produces an incorrect __setstate__ method. I've added printf in the __setstate__'s lambda or event directly into the pickle_factory's (line 327). It seems python calls never reach those.

Python code, second assert raising an error:

 a = C.toto()
 assert a.xx == 1
 a.__setstate__({'xx': 2, 'yy': 3})
 assert a.xx == 2

c++ code:

    struct Toto
    {

        int xx = 1;
        float yy = 1.0f;
    };

    template <typename T>
    inline T _get(char const * name, pybind11::dict & kwa, T deflt)
    { return  kwa.contains(name) ? kwa[name].cast<T>() : deflt; }

   PYBIND11_MODULE(example, mod) {
        using namespace pybind11::literals;
        pybind11::class_<Toto>(mod, "toto")
            .def(pybind11::init([](pybind11::kwargs d)-> Toto
                    { return { _get<int>("xx", d, 1), _get<float>("yy", d, 1.0f)};  }))
            .def_readwrite("xx", &Toto::xx)
            .def_readwrite("yy", &Toto::yy)
            .def(pybind11::pickle([](Toto const & self)
                    {
                        pybind11::dict x;
                        x["xx"] = self.xx;
                        x["yy"] = self.yy;
                        return x;
                    },
                    [](pybind11::dict d) -> Toto
                    { return { _get<int>("xx", d, 1), _get<float>("yy", d, 1.0f)};  }));
   }

Start by reproducing the supplied Python assertions with the C++ binding on the reported pybind11 2.2.3 and Python 3.6.3 setup. Inspect pickle_factory around line 327, which the report identifies, and trace why the setstate callback is not reached. Done means the second assertion passes after calling setstate.