Error in defaulting Org Key
You are right. Even I faced the same issue. Even after assigning P0001-PLANS, it was showing me as personnel area as default value, which was weird. Not sure if I can call it as a bug.
However, here's what I did as a workaround. I changed the entry Organizational key: Creation rules to a different field (example payroll area), saved the table and exit. Checked PA30 to see if the new value was getting correctly defaulted and payroll area was getting defaulted. Again went to the creation rules and updated it with same P0001-PLANS, saved and exit. And this time it worked. Position was getting defaulted. Weird it was, but it worked
Try it out if it works for you.