Slurm job expansion using the C API - slurm

Question

I sent this question a few months ago to the slurm-dev list, but it is still unsolved.
The problem is: after trying to change the job size as describes the FAQ, I wanted to do it programatically using the API.
Everything seems to work fine before the step of updating the environment variables.
When I launch the application this is what I get:
$ salloc -N1 mpiexec -n 1 ./jobExpansion
salloc: Granted job allocation 559
srun: error: Only allocated 1 nodes asked for 4
In the squeue I can see that the allocation has changed, but srun cannot see the changes.
I continued debugging and if I executed:
$ salloc -N1
$ export SLURM_NODELIST=n04,n06,n00,n01
$ export SLURM_NNODES=4
$ mpiexec -n 1 ./jobExpansion
It worked.
So, I don't want to overwhelm with the complete code but, just in case you could help me I paste here the parts of the resizing:
slurm_init_job_desc_msg(&job);
job.user_id = getuid();
job.min_nodes = hostsToExpand;
job.dependency = (char *) malloc(sizeof (char)*20);
sprintf(job.dependency, (char *) "expand:%s", pID);
//$ salloc -N4 --dependency=expand:$SLURM_JOBID
slurm_alloc_msg_ptr = slurm_allocate_resources_blocking(&job, 0, NULL);
//$ scontrol update jobid=$SLURM_JOBID NumNodes=0
slurm_init_job_desc_msg(&job_update);
job_update.job_id = slurm_alloc_msg_ptr->job_id;
job_update.min_nodes = 0;
slurm_update_job(&job_update);
//exit
slurm_kill_job(slurm_alloc_msg_ptr->job_id, 9, 0);
//$ scontrol update jobid=$SLURM_JOBID NumNodes=ALL
slurm_init_job_desc_msg(&job_update);
job_update.job_id = procID;
job_update.min_nodes = INFINITE;
slurm_update_job(&job_update);
Everything points out the environment variables but I am not sure how to properly update them.
Thank you.
EDITED
If somebody would like test what I've said, here is the repository:
git clone https://siserte#bitbucket.org/siserte/slurm-job-expansion-test.git