luabind 'Trying to use unregistered class' on return

Question

I'm currently using luabind to bind a class (sf::Time from SFML 2.0 to be exact), and I keep getting an exception from luabind. Here is my binding code:

            using namespace luabind;

            module(L, "system")
            [
                class_<sf::Time>("Time")
                    .def(constructor<>())
                    .def("toSeconds", &sf::Time::asSeconds)
                    .def("toMilliseconds", &sf::Time::asMilliseconds)
                    .def("toMicroseconds", &sf::Time::asMicroseconds)
                    .def(self == other<sf::Time>())
                    .def(self < other<sf::Time>())
                    .def(self <= other<sf::Time>())
                    .def(self - other<sf::Time>())
                    .def(self + other<sf::Time>())
                    .def(self * float())
                    .def(self / float())
                    .scope
                    [
                        def("seconds", &sf::seconds),
                        def("milliseconds", &sf::milliseconds),
                        def("microseconds", &sf::microseconds)
                    ],
...

My lua code is:

local t = system.Time.seconds(10)

The signature of sf::seconds is:

sf::Time sf::seconds(float)

I've tried wrapping the call to sf::seconds in my own function that returns sf::Time, and I tried using sf::Time* as the return value as well. No matter what, I keep getting the error.

Any ideas?

EDIT:

I have tested the class its self, and i can create it in Lua using system.Time(), no problem. All the methods work correctly, but system.Time.seconds and the other static methods don't work.