CXTPDatePickerControl OnButtonClick

I'm trying to add functionality to a button added to my CXTPDatePickerControl via the AddButton method.  From what I can tell, I should be able to override the OnButtonClick method to do this.  What I have works, more or less, except that I'm trying to use this control as it is used in the provided sample, that is as part of a CComboBox and popup window.  The normal Today and None buttons, after they are clicked, cause the call to GoModal to return.  When my custom button is clicked, the actions I've coded execute (i.e. the date selection changes), but the GoModal call doesn't return.  I'm sure there is some call or message sending I'm missing, but I don't know what it is.  Can you tell me what I'm missing?

Here is the code I have so far in my OnButtonClick method (be gentle, I'm new to MFC and C++ in general):

if(id == IDS_ButtonText){

NMHDR d; 
d.code = NM_CLICK;
d.idFrom = IDS_ButtonText;
d.hwndFrom = m_hWnd;
COleDateTime birthday;
birthday.ParseDateTime("4/30/1979");
EnsureVisible(birthday);
Select(birthday);
SendMessageToParent(XTP_NC_DATEPICKER_BUTTON_CLICK, &d);
}
else{CXTPDatePickerControl::OnButtonClick(id); }