Is see no problems wrt to the exchanged stanzas. The initial presence (XEP-45 7.2.2)
<presence id='yBjsG-11' to='aaaaa_og6@conference.bzwang/bbbbb'><x xmlns='http://jabber.org/protocol/muc'><history maxstanzas='20'/></x></presence>
is answered with
<presence id="yBjsG-11" to="bbbbb@bzwang/Smack" from="aaaaa_og6@conference.bzwang/bbbbb"><x xmlns="http://jabber.org/protocol/muc#user"><item jid="bbbbb@bzwang/Smack" affiliation="none" role="participant"/></x></presence>
which should be matched by the responseFilter in MultiUserChat's join() method, which is then used in the packet collector.
Note that the filter displayed in the screenshot does match a different MUC: aaaaa_0z2. Also note that alpha7 is the most recent version of Smack 4.1, But don't think that it should matter in this case. I've also deleted your comment on github. Let's keep the discussion in one place.