Use of GetClientRect in activeX - inconsistent results

I've inherited some activeX controls that I have been endeavoring to extend.  Much to my annoyance, the changes are becoming a career path.  I will preface my question with the warning that the control in question may have never worked correctly to begin with....

As with all activeX controls, there are two modes of operation - design mode and user mode.  Design mode seems to work fine.  User mode seems to be the braindead path.  I've attached the code below.  Basically, the control redraws itself incorrectly, not filling in the entire window region.  If you look at the code below, we have two handlers - OnPaint does the drawing in user mode, OnDraw handles design mode.  Design mode always works, and I've tracked it down to the GetClientRect call.

In design mode, when I resize things, GetClientRect returns the new size of the control.  So, all of my centering, etc plays correctly.  In user mode, the GetClientRect returns only the first window size.  Resizing is ignored.  I should point out that my test results are from using the activeX control test container, but the results seem to play out in actual use.

My conclusion is that this behavior has been there for many years.  Because we don't resize or do serious drawing at runtime, we never ran into this issue.  I'd like someone to tell me if GetclientRect is being used correctly, or shine some light on this issue maybe with some additional questions.

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void CMyButton::OnPaint() 
{
   CPaintDC dc(this); // device context for painting
	
   // Get client rect.
   CRect rc;
   GetClientRect(rc);
 
   DrawButton(&dc, rc, some_app_data, GetState());
 
   // Do not call CButton::OnPaint() for painting messages
}
 
void CMyButton::OnDraw(CDC* pdc, const CRect& rcBounds, const CRect& rcInvalid)
{
   DoSuperclassPaint(pdc, rcBounds);
 
   if (AmbientUserMode())
   {
      // Control is in run-mode.
      // If control window has not been created, then create it.
      if (!IsWindow(m_NButton.m_hWnd))
      {
         CRect rc;
         GetClientRect(rc);
 
         // A class 'CMyButton' is derived from the standard Microsoft
         // CButton class.  The CMyButton class is the control when in
         // run-mode.
         m_MyButton.Create(_T("MyButton"),
	   WS_CHILD | WS_VISIBLE | BS_OWNERDRAW | GetStyle(),
           rc, this, 0);
 
         m_MyButton.EnableWindow(m_buttonData.bEnabled);
      }
 
      // The button will be drawn in the CMyButton object.
   }
   else
   {
      // Control is in design-mode.
      DrawButton(pdc, rcBounds, m_buttonData, 0x00);
   }
}