Why isn't the AS3 garbage collector picking this up?

I started running into serious issues with the garbage collector partially picking this up, but still leaving most of the object up and running in the background without a reference:

m_win = new MyWindow(arr);
m_win.open();
m_win.addEventListener(Event.CLOSE, onClose);

.
.
.

private function onClose(pEvent:Event😞void
{
    m_win.removeEventListener(Event.CLOSE, onClose);
    m_win.close();
    m_win = null;
    // RAM usage for m_win is only reduced about 20-40%.  I can see the garbage
    // collector has run as a result of that reduction, but the other 60-80% are
    // a serious problem.
}

That's the only event listener I have added to m_win, and that's the only reference my code has to m_win.  MyWindow is basically a standalone AIR project (although it's nested in a different class than its own Main class to adapt it to work for this scenario; otherwise the same). MyWindow has NetConnections, NetStreams, and such that were kept live after the garbage collector would run.

So one of the first things I tried was to go in and disconnect its NetConnections and NetStreams.  But that didn't work.  Then I came across these blogs:

http://tomgabob.blogspot.com/2009/11/as3-memory-management.html

I found the link for that in another blog from another guy who had trouble with the same thing:  Supposedly if AS3's garbage collector finds an "island" that has reached a critical mass (in my experience, maybe 30 MB?), it just refuses to do anything with it.  So I went with this guy's recommendation and at least attempted to null out every reference, remove every event listener, call removeAllElements() and/or removeChildren() where necessary, and call "destructor" functions manually all throughout MyWindow, the sole exception being the Main class that isn't really used for m_win.

It didn't work, unless I messed up.  But even if I left a couple of stones unturned, it should have still broken up the island more than enough for it to work.  I've been researching other causes and work-arounds for this problem and have tried other things (such as manually telling the garbage collector to run), but nothing's cleaning the mess up properly.  The only thing that has worked has been to disconnect the NetConnection/NetStream stuff on the way out, but a good 25-30 MB is remaining uncollected.

How can this be fixed?  Thanks!