Why would a ProxyLookup fail to propagate LookupEvents from its delegates?

In my NetBeans-based application, I use a ProxyLookup is used to provide a "grab-bag" of instances originally associated with a some Node. In the case of a collection-like node, I use it to simply delegate to the sub-nodes' Lookup's to maintain an useful illusion of a container.

What surprised me was that none of my LookupListener instances attached to the proxy were being notified when changes happened in a delegate's Lookup?! Have you seen this, too?

Here's a JUnit test to demonstrate the puzzle, where I skip the formalities for brevity:

...

 class EventCountingLookupListener implements LookupListener {
     private int count_ = 0;
     public EventCountingLookupListener(Lookup.Result result) {
         result.addLookupListener(this);
     }
     public void resultChanged(LookupEvent ev) {
         ++count_;
     }
     public int count() {
         return count_;
     }
 }

 public void testProxyLookupNoEvents() {

     InstanceContent ic = new InstanceContent();
     AbstractLookup al = new AbstractLookup(ic);
     Lookup.Result result0 = al.lookupResult(String.class);
     EventCountingLookupListener ll0 = new EventCountingLookupListener(result0);

     Lookup proxy = new ProxyLookup(al);

     Lookup.Result result = proxy.lookupResult(String.class);
     EventCountingLookupListener ll = new EventCountingLookupListener(result);

     ic.add("hello1");
     assertEquals(1, ll0.count()); // OKAY: 1 event encountered in the delegate as expected
     assertEquals(1, ll.count()); // FAILURE: No events encountered in the proxy!!
 }
...

Thanks to my kind colleague Tom Wheeler who also helped me to review the test code, we have now an open issue #136866 at the NetBeans Community website. Hopefully, some of the experts there will be able to shed a bit of light.

Luckily, I soon found a workaround (soon enough to prevent having to redesign my work :) As it turns out, simply calling proxy.lookupAll() before the events are expected, was sufficient to get the "correct" behavior:

...
 public void testProxyLookupEventsWithLookupAllBeforeObtainingResult() {

     InstanceContent ic = new InstanceContent();
     AbstractLookup al = new AbstractLookup(ic);

     Lookup proxy = new ProxyLookup(al);
  
       // NOTE: proxy.lookupAll() does the "magic" here ...
       // ... before any listeners have been attached to any of the
       // proxy's Lookup.Result-s
       assertEquals(0, proxy.lookupAll(String.class).size());

     Lookup.Result result = proxy.lookupResult(String.class);
     EventCountingLookupListener ll = new EventCountingLookupListener(result);

     ic.add("hello1");
     assertEquals(1, ll.count()); // OKAY: 1-st event encountered!

     ic.add("hello2");
     assertEquals(2, ll.count()); // OKAY: 2-nd event encountered!
 }
...

Is this a feature or a bug?