[IndexedDB] Transactions during window.unload?

In a page utilizing Indexed DB, what should the expected behavior be for an
IDBTransaction created during the window.onunload event callback?

e.g.

window.onunload = function () {
  var transaction = db.transaction('my-store', IDBTransaction.READ_WRITE);
  transaction.onabort = function () { console.error('aborted'); };
  transaction.oncomplete = function () { console.log('completed'); };

  var request = transaction.objectStore('my-store').put('value', 'key');
  request.onsuccess = function () { console.log('success'); };
  request.onerror = function () { console.error('error'); };
};

I'm not sure if there's a spec issue here, or if I'm missing some key
information (from other specs?).

As the execution context is being destroyed, the database connection would
be closed. (3.1.1). But the implicit close of the database connection would
be expected to wait on the pending transaction (4.9, step 2). As written,
step 6 of "lifetime of a transaction" (3.1.7) would kick in, and the
implementation would attempt to commit the transaction after the unload
event processing was completed. If this commit is occurring asynchronously
in a separate thread/process, it would require that the page unload
sequence block until the commit is complete, which seems very undesirable.

Alternately, the closing page could abort any outstanding transactions.
However, this leads to a race condition where the asynchronous commit could
succeed in writing to disk before the abort is delivered.

Either way, I believe that that after the unload event there are no more
spins of the JS event loop, so therefore none of the events
(abort/complete/success/error) will ever be seen by the script.

Is there an actual spec issue here, or is my understanding just incomplete?