Why is it that when doing DDX thru UpdateData it doesn't generate any control notification messages?

For example, i have a combo box on a form and when the user changes the selection it should cause changes to other controls (e.g. disable this edit box, enable that one, etc.) which i do thru the CBN_SELCHANGE message handler.

But... when i do DDX to set the combo box selection it does not generate a CBN_SELCHANGE message. WHY?!?!?!?! And how do i get around this piece of MFC stupidity?