test_vtkreader_2d3d fails due to assert

test_vtkreader_2d3d: /data/src/dune-alugrid/dune/alugrid/impl/serial/gitter_mgb.cc:759: void ALUGrid::MacroGridBuilder::finalize(): Assertion `((hface3_GEO *)(*i).second)->ref == 2' failed.

Maybe something is wrong with the grid file? The test passes however, if assertions are disabled.