http://fisheye.igniterealtime.org/browse/smack/trunk/source/org/jivesoftware/sma ckx/XHTMLText.java?r=7071#l133 shows that smack appends "<br>" where it should "<br/>" as postulated by XEP-71.
ATM I have to
String xhtmlBody = message.generateXHTMLText().toString();
xhtmlBody = xhtmlBody.replace("<br>", "<br/>"); //fix for smackx problem
to workaround this Bug.
Logged as SMACK-329.
In the future, please add the tag bug_report to your post