case WM_LBUTTONDOWN :
case WM_LBUTTONUP :
{
         // need to check to make sure the mouse click happens on the button
         if ( InternalHitTest(lParam) == FALSE )
         {
                  if (message == WM_LBUTTONDOWN)
                       return 0;  // just leave
                  // If we are inside a corner but outside the button,
                  // tell button proc that we are outside.
                  lParam = 0xffffffff;       // put the pt at (-1,-1)
         }
         return CallWindowProc(fnOrgBtn, hWnd, message, wParam, lParam);
}