Saturating message queue?

I was interested in timing how long it took for a parent and child thread to
exchange a series of window messages. I thought I would start with the Frame
and View in the main thread of a doc/view sdi app for simplicity.

I set up a menu item to initiate a loop. Then the Frame and View exchange a
token until the token is incremented to a certain value. However, it hangs
if I use a token value of more than 20. Am I doing something wrong? Is
"SendMessageToDescendants" an inappropriate choice? Is the message queue
"saturating"? ... which would seem odd since the app is using "SendMessage"
rather than "PostMessage"?

// MainFrame handles menu command to initiate
void CBbMainFrame::OnTimeMessaging()
{
  SendMessageToDescendants(UWM_BB_FRAME_TO_VIEW, 1, 0);
}

// View handles message and checks token value
// 20 or less is ok, hangs with 21
LRESULT CBbView::OnBbFrameToView(WPARAM token, LPARAM)
{
  TRACE1("View:FrameToView %d\n", token);
  if (token == 1) {
    HiResTimerStart(); // Uses QueryPerformanceCounter
  }
  if (token < 20) {
    m_pFrame->SendMessage(UWM_BB_VIEW_TO_FRAME, token, 0);
  }
  else {
    double elapsed = HiResTimerElapsedMillis();
    CString csMsg;
    csMsg.Format("20 loops Token: %d elapsed: %.3f\n", token, elapsed);
    AfxMessageBox(csMsg);
  }
  return 0;
}

// Frame handles message, increments token, and sends another message
LRESULT CBbMainFrame::OnBbViewToFrame(WPARAM token, LPARAM)
{
  TRACE1("Frame:ViewToFrame Token: %d\n", token);
  SendMessageToDescendants(UWM_BB_FRAME_TO_VIEW, (token+1), 0);
  return 0;
}