Widget's Resize method not called when size changes

[Fred]

I have written a Grid widget that is a subclass of XmDrawingArea. An
instance of this widget is a child of an XrtTabManager (I have also
used an XmNotebook, with same results). When this child is not the
visible page, the app does some processing that causes the Grid widget
to resize. However, the Grid's Resize method is not invoked.

If I register an event handler on the widget using
StructureNotifyMask; the event handler proc does get called with event
type ConfigureNotify and the widget's size has changed.

Why am I getting a ConfigureNotify event but not a Resize when the
size has changed?

(Also posted to MotifZone forum)
--
Fred K