In job_func.c, there are two places where job_purge is called, like so:

job_purge(pjob); 
*pjobp = NULL;

where pjob = *pjobp. However, this pattern leaves pjob pointer at a dead
structure, and mean that later NULL tests on job are incorrect. Simply doing
this:

job_purge(pjob);
*pjobp = NULL;
 pjob = NULL;

resolves the problem.