self-assign-overloaded warning in Python code

When compiling dune-istl with Python bindings enabled, Clang with some additional warnings gives me:

/home/gruenich/dune/complete/dune-common/dune/python/common/densevector.hh:159:31: warning: explicitly assigning value of variable of type 'const pybind11::detail::self_t' to itself [-Wself-assign-overloaded]
      cls.def( pybind11::self -= pybind11::self );
               ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
In file included from /home/gruenich/dune/complete/dune-istl/python/dune/istl/_istl.cc:11:
In file included from /home/gruenich/dune/complete/dune-istl/dune/python/istl/bcrsmatrix.hh:9:
In file included from /home/gruenich/dune/complete/dune-common/dune/python/common/fvecmatregistry.hh:6:
In file included from /home/gruenich/dune/complete/dune-common/dune/python/common/fmatrix.hh:15:
/home/gruenich/dune/complete/dune-common/dune/python/common/densematrix.hh:54:31: warning: explicitly assigning value of variable of type 'const pybind11::detail::self_t' to itself [-Wself-assign-overloaded]
      cls.def( pybind11::self -= pybind11::self );
               ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
In file included from /home/gruenich/dune/complete/dune-istl/python/dune/istl/_istl.cc:11:
In file included from /home/gruenich/dune/complete/dune-istl/dune/python/istl/bcrsmatrix.hh:20:
/home/gruenich/dune/complete/dune-istl/dune/python/istl/bvector.hh:159:31: warning: explicitly assigning value of variable of type 'const pybind11::detail::self_t' to itself [-Wself-assign-overloaded]
      cls.def( pybind11::self -= pybind11::self );
               ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~

The code looks suspicious. Is this intended?