Can a WeakRef be overseen?

I have added some debug output to the wrapper

PROCEDURE CleanupPlan (<* UNUSED *> READONLY w: WeakRef.T; r: REFANY) =
  BEGIN
    IO.Put("Cleanup_Plan\n");
    FFTWLongRealRaw.DestroyPlan(NARROW(r, Plan)^);
  END CleanupPlan;

that I use as a cleanup procedure for a WeakRef:

  ...
    plan^ := FFTWLongRealRaw.PlanDFT1D(n, in[0], out[0], dirToSign[sign],
                                       LOOPHOLE(flags, C.unsigned_int));
    EVAL WeakRef.FromRef(plan, CleanupPlan);
    RETURN plan;
  ...

Suprisingly the "Cleanup_Plan" won't be printed in most cases.  I use only
short test programs that some computations and then quit immediately. Does
the result mean that the wrapper wasn't called or does it mean that the
output of the text failed?