[boost] [mpl] is_lambda_expression bug?

The compile-time assertion fails in the following program. I have tried with more than one version of boost including 1.53. Is it a bug? Shall I report it? -------------------------------------------------- #include <boost/mpl/assert.hpp> #include <boost/mpl/lambda.hpp> #include <boost/mpl/plus.hpp> namespace mpl = boost::mpl; struct MetafunctionClass { template<typename T1, typename T2> struct apply { typedef typename mpl::plus<T1,T2>::type type; }; }; BOOST_MPL_ASSERT((mpl::is_lambda_expression<MetafunctionClass>)); int main(int argc, char * argv[]) { } --------------------------------------------------