Yes, if this path runs multiple times, we release multiple times.  But an ObjectInserter (and an ObjectReader) are required to support using the object again after a release.  That is, the following is completely legal:

  ObjectInserter oi = ....;
  oi.insert(...);
  oi.release();

  oi.insert(...);
  oi.release();

  oi.release();
  oi.insert(...);
  oi.release();

So even a back-to-back release without any use between them is valid.  Its just a minor CPU time waste.