SMACK-614 and SMACK-615. A potential fix for SMACK-614 has been included in asmack-android-8-4.0.6-SNAPSHOT-2014-11-08.jar. Please test and report back.
I also tend to mark SMACK-615 as "won't fix", changing the username+password using the same connection instance will become impossible anyways once ConnectionConfiguration becomes immutable and carries this information (which it should have done in the first place).