Muc mam can not before

here is my iq.
Single chat is right.

<iq type="set" to="test03@conference.com.innovate.ygoa" id="7B297358-FA84-4C43-BFEC-3FC0831A56E1">
  <query xmlns="urn:xmpp:mam:1">
    <x xmlns="jabber:x:data" type="submit">
      <field var="FORM_TYPE" type="hidden">
        <value>urn:xmpp:mam:1</value>
      </field>
    </x>
    <set xmlns="http://jabber.org/protocol/rsm">
      <max>3</max>
      <before/>
    </set>
  </query>
</iq>

The order of the returned messages is incorrect, and the correct result should be in reverse order. But the server returns the order. For example: the messages are 1, 2, 3, 4, 5. According to the iq I sent back should be 5,4,3. But in fact return is 1,2,3