sys-cluster/native-mpi does install some mpi environment, but doesn't install or enforce installation of any of the mpi libraries. virtual/mpi accepts native-mpi as one of it's possible alternatives. When any packages (in particular sci-libs/parmgridgen in my case) requires virtual/mpi and tries to compile e.g. against libmpich, this leads to a compile error, as this lib cant be found. So either native-mpi has to install/enforce installation of libs, or virtual/mpi has to unlist it.
Its intended by design. This package was for prefix only if you use it with already installed system mpi on hpc cluster. So its not a bug =D
Please explain - seems I misunderstand completely. What's not a bug, and why?