When we schedule a mailing in civimail we use a normal group (not a smart group) as the target audience for this mailing. Prior to 4.6.2 (we think), we could change the group before the mailing was send (even though it was scheduled) and the changes to the group would be taken into account when the actual sending of the mail occurred.
We are now on version 4.6.4 and looked into the database a bit to see what happens when somebody schedules a mailing. It seems as the schedule button fills the "civicrm_mailing_recipients" table and this table is used when the mailing actually starts. So adding a contact to the group(s) you used does nothing.
Is this behavior correct/by design? And is there a workaround to get the latest group members when the mailing actually starts?