Strange behavior involving mpi and symbolic links when using singularity on WSL

[ettaka]

I am running WSL Ubuntu on Windows 11. I have a script kqclib.sh on host machine to invoke commands in singularity image (kqclib):

#!/bin/bash
dir="$(dirname "$(readlink -f "${BASH_SOURCE[0]}")")"
img="kqclib"
if [ "$(basename "$0")" = "kqclib" ]; then
        cmd="python"
else
        cmd=$(basename "$0")
fi

# Check if running on WSL and use higher compatibility then
if grep -qi "microsoft" /proc/version; then
  echo running: singularity exec --containall --home "${PWD}" "${dir}/${img}" "$cmd" "$@"
  singularity exec --containall --home "${PWD}" "${dir}/${img}" "$cmd" "$@"
else
  echo running: singularity exec --home "$HOME" "${dir}/${img}" "$cmd" "$@"
  singularity exec --home "$HOME" "${dir}/${img}" "$cmd" "$@"
fi

So if I have a symbolic link like this

lrwxrwxrwx 1 eelis eelis 57 Aug  2 14:35 ElmerSolver_mpi -> kqclib.sh

and I run it, everything works as expected:

✗ ElmerSolver_mpi
running: singularity exec --containall --home /home/eelis/git/KQCircuits/singularity/bin /home/eelis/git/KQCircuits/singularity/libexec/kqclib ElmerSolver_mpi
ELMER SOLVER (v 9.0) STARTED AT: 2023/08/03 11:45:47
ParCommInit:  Initialize #PEs:            1
MAIN: OMP_NUM_THREADS not set. Using only 1 thread per task.
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Version: 9.0 (Rev: 114ceed02, Compiled: 2023-08-02)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN:  MMG library linked in.
MAIN:  Lua interpreter linked in.
MAIN:  Zoltan library linked in.
MAIN: =============================================================

Now, if I run that with MPI, I get individual processes

✗ mpirun -np 2 ElmerSolver_mpi
running: singularity exec --containall --home /home/eelis/git/KQCircuits/singularity/bin /home/eelis/git/KQCircuits/singularity/libexec/kqclib ElmerSolver_mpi
running: singularity exec --containall --home /home/eelis/git/KQCircuits/singularity/bin /home/eelis/git/KQCircuits/singularity/libexec/kqclib ElmerSolver_mpi
ELMER SOLVER (v 9.0) STARTED AT: 2023/08/03 11:47:56
ELMER SOLVER (v 9.0) STARTED AT: 2023/08/03 11:47:56
ParCommInit:  Initialize #PEs:            1
MAIN: OMP_NUM_THREADS not set. Using only 1 thread per task.
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Version: 9.0 (Rev: 114ceed02, Compiled: 2023-08-02)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN:  MMG library linked in.
MAIN:  Lua interpreter linked in.
MAIN:  Zoltan library linked in.
MAIN: =============================================================
ParCommInit:  Initialize #PEs:            1
MAIN: OMP_NUM_THREADS not set. Using only 1 thread per task.
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Version: 9.0 (Rev: 114ceed02, Compiled: 2023-08-02)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN:  MMG library linked in.
MAIN:  Lua interpreter linked in.
MAIN:  Zoltan library linked in.
MAIN: =============================================================

If I run the same in my Ubuntu virtual box, I get the correct behaviour (2 parallel environments, #PEs 2)
Or if I run without the link in WSL, I also get the correct behaviour:

✗ singularity exec kqclib mpirun -np 2 ElmerSolver_mpi
ELMER SOLVER (v 9.0) STARTED AT: 2023/08/03 11:50:37
ELMER SOLVER (v 9.0) STARTED AT: 2023/08/03 11:50:37
ParCommInit:  Initialize #PEs:            2
ParCommInit:  Initialize #PEs:            2
MAIN: OMP_NUM_THREADS not set. Using only 1 thread per task.
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Version: 9.0 (Rev: 114ceed02, Compiled: 2023-08-02)
MAIN:  Running in parallel using 2 tasks.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN:  MMG library linked in.
MAIN:  Lua interpreter linked in.
MAIN:  Zoltan library linked in.
MAIN: =============================================================

Does anyone know why this is happening?