Currently in SM 15.7, when you "Reply All", to a message that contains additional recipients in the "To" field in the original message, the original sender is added to the "To" field in the reply -- but at the end of the list.  The original sender should instead be inserted as the first name/address in the "To" field, not the last.  It's a very minor point, but I've had more than a few clients complain about it, especially when they sort their "Sent Items" messages by the "To" field and cannot find the message they're looking for.