There is an easy workaround/fix for this:
su - zimbra
cd /opt/zimbra/bin
EDIT zmsaslauthdctl
CHANGE:
${zimbra_home}/cyrus-sasl-2.1.21.ZIMBRA/sbin/saslauthd -a zimbra
TO:
${zimbra_home}/cyrus-sasl-2.1.21.ZIMBRA/sbin/saslauthd -r -a zimbra
(Basically add a -r to keep the domain)
Then run /opt/zimbra/bin/zmsaslauthdctl restart |