Update wxTextCtrl without disturbing scroll position
// k is line to update
// update is new line contents

        myTxtCtrl->Replace(
            myTxtCtrl->XYToPosition(0,k),
            myTxtCtrl->XYToPosition(0,k+1),
            update + L"n");

// the control has now scrolled to ensure line k is visible

myListCtrl->SetItem(k,0,update);