Error with markers on inner facets, 3D

Currently, TriTetMesh reports an error when one tries to generate meshes in 3D with markers on inner boundaries, see the attached script. The comments in tritetmesh/tetmesh/tetmesh.cpp say "Tetgen only saves the faces on the boundary together with any marker." However, TetGen is capable to handle also markers on internal facets (I think, they are PLC facets in the terminology of TetGen).

If I comment out the three lines in tritetmesh/tetmesh/tetmesh.cpp containing "if (!(con23.size(face)>1))", everything works fine and I also get markers on the internal facets.

Btw: Why are the tetrahedron attributes (and similarly, the triangle attributes for 2D meshes) saved as a double-MeshFunction? If I want to use them for integration in FEniCS, I have to convert them manually to a uint-MeshFunction, anyway.