Getting the most current Outlook AppointmentItem theme string value

I have problems accessing the actual typed text in the Subject field of the AppointmentItem. I created an Outlook 2010 add-in with a callback from a custom button from the ribbon. I can get the value of the Subject field, except that someone presses the button immediately after entering the topic (and does not change the focus of control). In these cases, I get the previous Subject value, not the recently entered value. (for a newly created meeting request, I get a null value)

   public void ToggleMeetingPlace_Callback(Office.IRibbonControl control)
    {
        if ((control!=null)&&(control.Id == "toggleMeetingPlace"))
        {
            var item = control.Context as Outlook.Inspector;
            if ((item != null) && (item.CurrentItem != null))
            {
                Outlook.AppointmentItem m_item = item.CurrentItem as Outlook.AppointmentItem;
                string subject = m_item.Subject;
                // some action
            }
        }
    }

, , : - m_item.Subject - m_item, , .

, , ... , .