Problem:
Birthday and anniversary attributes are not emptyed in OX, if emptied in UCS Setting the birthday or anniversary the change applies in OX but emptying the attribute does not apply.
Solution:
You can remove them manually. You have to adjust the context, if you are not using the default one.
root@ucs-ox:~# /opt/open-xchange/sbin/changeuser -c 10 -A oxadmin -P $(< /etc/ox-secrets/context10.secret) -u cscheini "--birthday="
root@ucs-ox:~# /opt/open-xchange/sbin/changeuser -c 10 -A oxadmin -P $(< /etc/ox-secrets/context10.secret) -u cscheini "--anniversary="